Visual Basic for Very Bright Kids - Part 4 - Programming with the .NET Framework

February 2007

Having Visual Basic without the ".NET Framework" is about as useful as a pen without ink. You can write all you wish, but you’re not going to achieve anything useful.

What is the .NET framework? It is a programming platform developed by Microsoft. Visual Basic was specifically written as a language that will use the .NET Framework. The framework is made up of two different things:

  1. A huge library of code that we can call from our Visual Basic programs. This saves us writing everything ourselves.

  2. A "runtime" module, which runs our programs for us when we’re ready (this happens invisibly - you don't need to worry about it)

When you write a Visual Basic program (or a program in any of the other .NET languages), you typically call some code that lives in the library, as well as writing some of your own code.

Bb330919.6c6d7e77-2a45-440b-838b-f8ba56345f7b(en-US,VS.80).png

There are so many classes in the .NET framework, and some of them are pretty complicated, so we certainly won't try to cover the whole thing here. Instead, this section's chapters go through some of the .NET framework classes that we think you'll find most useful. As you grow in experience, you'll find that there are certain classes that you use often and you'll get to know those ones well - like taking a favorite book out of the library - eventually you know just where to find it.

It's very important to realize that part III is not just for reading - these chapters include a lot of sample programs and you're supposed to try them all out for yourself and then try changing them to do new things.

How to Try Out the Examples

In the following chapters, whenever you see a block with the words "code for program ..." you can run that code using Visual Basic Express. Although most of these programs are short, they are all real working programs. Here are the steps you will normally follow:

  • Open Visual Basic Express. Select File -> Open Project and then browse to wherever you saved the example programs. Open any file with a ".vbproj" extension. (or you can use Windows Explorer to find the sample you want and simply double-click the .vbproj file.)

  • Press F5 to run the program (or click the green arrow)

How to Change and Extend the Examples

It's fine telling you "you can change the examples", but how do you know what to change them to? The examples show a few .NET Framework classes and methods being used - how do you know what other ones are available? There are a few ways to find out:

  • Look through the .NET Framework SDK Class Library included in Visual Basic Express's help. 

  • While programming in Visual Basic Express, to see the available classes, methods, fields, etc for a class, press the "." key directly after typing a namespace or class name. E.g. Type "Console." and you'll see a list of methods and other members available in the Console class.

Bb330919.23dd9937-2fd3-4178-ab7f-21cb8ae78226(en-US,VS.80).png

In the case of a method, if you type an open parenthesis at the end of the method name, you can also see the parameter types that the method expects. Often a method is written in a special way to allow different sets of parameters - then you can scroll through them by pressing the down and up arrow keys. The following example shows what happens when you type "Console.WriteLine(". Visual Basic Express shows that there are 18 different ways you can call WriteLine. In the picture below, we pressed the down arrow until we reached the 14th one.

Bb330919.6f6dd582-dfea-4ffb-9575-adba0cec2210(en-US,VS.80).png
Bb330919.d547e250-3cf4-478c-a471-520d6bd39eef(en-US,VS.80).png
System.Console

Introduction

The idea of a "Console" comes from the days when large mainframe computers were very popular. A company would have a giant computer hiding in some back room and the people outside would have a keyboard and a simple screen, called a console, which was hooked into the beast in the back room. These screens could not display true graphics – only text. The keyboard was the input device, sending information to the computer, and the console was the main output device, allowing to computer to send information back to the user.

Bb330919.0526ef15-d598-47b4-9790-7061f617e6e8(en-US,VS.80).png

The world moved on and these days most computers use displays that can show far more natural representations to people than lines of text – photographs for example.

There is often a need, however, to do things that don’t need to show anything fancy to the user. You may, for example, have a program which goes and fetches some data from an Internet server somewhere and puts it into a file on your pc. If all you need it to say is "busy fetching data" and then "done", why waste a whole lot of time and memory on a fancy user interface? It is for this reason that the .NET library offers us a class for easily writing console applications.

Don’t scoff at console applications, as if "they aren’t cool". In fact, you’ll find the really smart programmers get tired of wasting time with fancy interfaces and do most of their own work in console applications.

Of course, if you plan to write a program that someone else is going to use, you probably want to be a little kinder and give them something friendlier than a console interface.

Some Useful Methods

  1. Console.ReadLine – reads a line of text from the keyboard (or some other input device)

  2. Console.Read – reads a number from keyboard (or some other input device)

  3. Console.WriteLine – writes text to the screen (or other output device), starting on a new line

  4. Console.Write – writes some characters to the screen without starting a new line

Example Program 1

The following program simply writes the word "Yo!" to the screen and then waits for the ENTER key to be pressed.

Code for program 1

Imports System

Class PleaseSayYo

    Shared Sub Main()
        ' Write a word to the screen
        Console.Write("Yo!")

        ' Wait until enter is pressed
        Console.ReadLine()
    End Sub

End Class
Bb330919.bd6a4964-90b5-4860-af86-551845d81525(en-US,VS.80).png

Example Program 2

The following program

  • Asks the user to type in a word on the keyboard

  • Asks the user how many times the word should be written out

  • Writes out, on a new line each time, the word that was entered, as many times as was requested

Code for program 2

Imports System

Class WriteAFewLines

    Shared Sub Main()
        Console.WriteLine("Type in your favourite word : ")

        ' Store, in a string variable, the word that the user entered
        Dim favouriteWord As String = Console.ReadLine()

        Console.WriteLine("How many times shall I write it? ")

        ' Store, in an integer variable, the number they type in
        ' (And they'll get an error if they don't type a true number)
        Dim numberOfTimes As Integer = Convert.ToInt32(Console.ReadLine())

        ' Write the word out as many times as was requested
        For i As Integer = 0 To numberOfTimes - 1
            Console.WriteLine(favouriteWord)
        Next

        ' Wait until ENTER is pressed
        Console.ReadLine()
    End Sub

End Class
Bb330919.9fbf705e-a6e6-48a7-be4c-55cbb8e6ea27(en-US,VS.80).png
System.Windows.Forms

Introduction

If you want to write programs that look and feel like the ones you’re used to using in a Windows environment, you’ll most definitely want to use the classes in the System.Windows.Forms namespace. They allow you to work with buttons, list boxes, text boxes, menus, message boxes and a whole bunch of other "controls." Controls are things you place on a form – they either show things like text (a Label control) and pictures (a Picture Box control) or allow you to carry out actions such as selecting a value or clicking a button to move to another form. You’ll probably use the classes beneath System.Windows.Forms in most of your Visual Basic programs.

Obviously the idea of a "form" comes from the widely used paper form in the "real" world. A form is something which allows the placing of various things (text, pictures, entry boxes, etc.) in a well-organized layout. Generally, a person will read some information on the form and fill in some information in particular regions.

Bb330919.7bf0436f-3349-4c18-85cf-985e5772d9f7(en-US,VS.80).png

The idea on the computer is similar – a form allows the placing of text, pictures, entry boxes, buttons, etc, in a fashion which allows these to be precisely organized on the screen - very different to a console application, which can only handle lines of text following each other.

Microsoft has provided, in the .NET Framework class library, a huge number of "controls" for use on forms. Once you know how to place a control on a form, you can build up a snazzy application very quickly, simply by using these existing controls.

Some useful classes in the System.Windows.Forms namespace

The following are examples of classes with code for controls that you can place on your forms

  • Label

  • Button

  • ListBox

  • CheckBox

  • RadioButton

  • ListBox

  • Menu

  • TabControl

  • Toolbar

  • TreeView

  • DataGrid

  • PictureBox

  • RichTextBox

A note about working with the Windows Forms examples using Visual Basic Express

To play with the following examples in Visual Basic Express, you can select File -> Open Project and open the book's sample .vbproj programs from wherever you chose to save them on your computer's disk.

If, however, you want to type them yourself from scratch, you need to be aware that when you create a new "Windows Application" project, Visual Basic Express puts down some .vb files for you (named Form1.vb and Program.vb), and inserts some Visual Basic code so that you're ready to go. It actually creates for you a basic but fully functional program. While you're working with the examples below, to keep things simple, you should probably

  • delete Form1.vb and

  • replace the code in Program.vb with the code from the example you're working with

This is not necessary if you rather open the examples using File -> Open Project.

Example Program 3

Here’s an absolutely simple Windows forms application. All it does is to start a new form and write some text in the titlebar of the window.

Code for program 3

Imports System.Windows.Forms

Class SimpleWindowsForm
    Inherits Form

    ' The constructor method for our class
    Public Sub New()
        ' Set the window title
        Me.Text = "A really Simple Form"
    End Sub

    Shared Sub Main()
        ' Start a new instance of a forms application, using our class above
        Application.Run(New SimpleWindowsForm())
    End Sub

End Class
Bb330919.68b6cffa-8903-4b10-885b-1d3e5d2b3d45(en-US,VS.80).png

Example Program 4

This example is simple too, but takes us to the next level – placing a button on the form

Code for program 4

Imports System.Windows.Forms

Class SimpleWindowsFormWithButton
    Inherits Form

    Private button1 As Button

    ' The constructor method for our class
    Public Sub New()
        ' Set the window title
        Me.Text = "A simple form with a button"

        ' Add a button to the form's collection of controls
        ' Although the button says "click me", nothing happens when you do!
        button1 = New Button()
        button1.Text = "Click me"
        Me.Controls.Add(button1)
    End Sub

    Shared Sub Main()
        ' Start a new instance of a forms application, using our class above
        Application.Run(New SimpleWindowsFormWithButton())
    End Sub

End Class
Bb330919.413d98d8-e3a7-406b-9120-27a752282ffb(en-US,VS.80).png

Example Program 5

Having a button on the form is okay, but in the example above, nothing happens when the user clicks the button. Boring.

We need to write a method that will do something when the button is clicked - let’s just make it change the Title Bar text in this case. We call such a method an event handler, since it will watch for an event (a click in this case) and will then decide how to handle it. We also need to hook the button click event up to the event handler.

Code for program 5

Imports System
Imports System.Windows.Forms
Imports System.Drawing

Class FormWithWorkingButton
    Inherits Form

    ' The constructor method for our class
    Public Sub New()
        ' Set the window title
        Me.Text = "Simple form with working button"

        ' Add a button and hook it up to an event handler method
        Dim button1 As Button = New Button()
        button1.Text = "Click me"
        AddHandler button1.Click, AddressOf Button1_Click
        Me.Controls.Add(button1)
    End Sub

    Shared Sub Main()
        ' Start a new instance of a forms application, using our class above
        Application.Run(New FormWithWorkingButton())
    End Sub

    ' An event handler that will be run when the button is clicked
    Private Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs)
        ' Change the window title
        Me.Text = "Button was clicked"
    End Sub

End Class
Bb330919.6c99e945-505b-41b2-b43f-5ddf0a365098(en-US,VS.80).png

Example Program 6

Right, the program does all the basic stuff. Now let’s add a few other types of controls to the form, lay them out nicely and work with them a little. We'll use 4 control types: Button, ListBox, MessageBox and PictureBox.

Notice that, apart from System.Windows.Forms, we'll also use the System.Drawing namespace here. This is necessary because we're using a PictureBox - and working with images requires the Drawing classes.

Code for program 6

Imports System.Windows.Forms
Imports System.Drawing

Class MyForm
    Inherits Form

    ' Declare a listbox outside the methods, since we'll want to talk to it
    ' from more than one method
    Private listBox1 As ListBox

    ' The constructor method for our class
    Public Sub New()
            ' Create a picture box, put a picture in it and add it to this form
            Dim pictureBox1 As PictureBox = New PictureBox()
            pictureBox1.SizeMode = PictureBoxSizeMode.StretchImage
            Dim image1 As Bitmap = New Bitmap("../../images/seashore.jpg")
            pictureBox1.ClientSize = New Size(Me.Width, 100)
            pictureBox1.Image = DirectCast(image1, Image)
            Me.Controls.Add(pictureBox1)

            ' Create a button object, 
            ' set some of it's properties and add it to the form
            Dim button1 As Button = New System.Windows.Forms.Button()
            button1.Location = New System.Drawing.Point(10, 120)
            button1.Text = "Click me"
            AddHandler button1.Click, AddressOf button1_Click
            Me.Controls.Add(button1)

            ' Create a listbox object, 
            ' set some of it's properties and add it to the form
            listBox1 = New System.Windows.Forms.ListBox()
            listBox1.Location = New System.Drawing.Point(10, 160)

            listBox1.Items.Add("Sparkly")
            listBox1.Items.Add("Dull")
            listBox1.Items.Add("Vivacious")
            listBox1.Items.Add("Plain")
            listBox1.Items.Add("Outstanding")

            listBox1.SelectedIndex = 3
            Me.Controls.Add(listBox1)

    End Sub

    ' An event handler method that will run when the button is clicked
    Private Sub button1_Click(ByVal sender As Object, ByVal e As System.EventArgs)
            ' Show a message indicating which item in the listbox is selected
            MessageBox.Show(Me, "You have selected " _
                  & listBox1.SelectedItem.ToString(), _
                  "Notification", MessageBoxButtons.OK)
    End Sub

    Shared Sub Main()
            ' Start a new instance of a forms application, using our class above
            Application.Run(New MyForm())
    End Sub

End Class
Bb330919.da530f93-393b-4d00-b0b1-91b98ce8552b(en-US,VS.80).png

Example Program 7

Okay, now let’s get wild. To illustrate how to use some of the other controls, we’ll write one really large program including many useful controls. This will make the code scarily long, but it will be a useful program for you to refer back to when you need to use a particular control.

You don't have to read the entire program in detail, but when you're interested in using, for example, a CheckBox, come back to this program, find the parts that talk about CheckBox and study those parts.

Notice that in order to use the PictureBox and the DataGridView in interesting ways, we're also going to use the namespaces System.Drawing, System.Data and System.Xml.

Code for program 7

Imports System
Imports System.Windows.Forms
Imports System.Drawing
Imports System.Data
Imports System.Xml

Class FormWithManyControls
    Inherits Form

      Private treeView1 As TreeView
      Private panel1 As Panel
      Private checkBox1 As CheckBox, checkBox2 As CheckBox
      Private radiobutton1 As RadioButton, radioButton2 As RadioButton
      Private listBox1 As ListBox

    ' The constructor method for our class
    Public Sub New()

        ' Set window title and size
        Me.Text = "A form dealing with many types of controls"
        Me.Width = 700
        Me.Height = 500

        ' Add a tree view as a kind of menu
        treeView1 = New TreeView()
        treeView1.BackColor = Color.BurlyWood
        treeView1.Dock = DockStyle.Left
        AddHandler treeView1.AfterSelect, AddressOf treeView1_AfterSelect

        Dim tn As TreeNode = New TreeNode("Controls")
        tn.Expand()

        tn.Nodes.Add(New TreeNode("[Wipe clean]"))
        tn.Nodes.Add(New TreeNode("Label"))
        tn.Nodes.Add(New TreeNode("Button"))
        tn.Nodes.Add(New TreeNode("CheckBox"))
        tn.Nodes.Add(New TreeNode("RadioButton"))
        tn.Nodes.Add(New TreeNode("ListBox"))
        tn.Nodes.Add(New TreeNode("TextBox"))
        tn.Nodes.Add(New TreeNode("TabControl"))
        tn.Nodes.Add(New TreeNode("DataGridView"))
        tn.Nodes.Add(New TreeNode("MainMenu"))
        tn.Nodes.Add(New TreeNode("ToolBar"))
        tn.Nodes.Add(New TreeNode("PictureBox"))
        tn.Nodes.Add(New TreeNode("RichTextBox"))

        treeView1.Nodes.Add(tn)

        Me.Controls.Add(treeView1)

        ' Add a panel to put all the other controls on
        panel1 = New Panel()
        panel1.Dock = DockStyle.Right
        panel1.BorderStyle = BorderStyle.Fixed3D
        panel1.Width = Me.Width - treeView1.Width

        Me.Controls.Add(panel1)

    End Sub

    ' An eventhandler that runs when something in the treeview is selected
    Private Sub treeView1_AfterSelect(ByVal sender As Object, _
            ByVal e As System.Windows.Forms.TreeViewEventArgs)

        ' Do something appropriate for whichever node was clicked
        If e.Node.Text = "[Wipe clean]" Then
            ' Wipe the panel clean of any controls
            panel1.Controls.Clear()

        ElseIf e.Node.Text = "Button" Then
            ' Add a button to the panel
            Dim button1 As Button = New Button()
            button1.Text = "I'm a button"
            button1.Location = New Point(150, 80)
            AddHandler button1.Click, AddressOf button1_Click

            panel1.Controls.Add(button1)

        ElseIf e.Node.Text = "Label" Then
            ' Add a label to the panel
            Dim label1 As Label = New Label()
            label1.Text = _
                  "This is a label. Labels are simply used " _
                  & "to write text at a point on the screen"
            label1.Location = New Point(150, 10)
            label1.Width = 400
            AddHandler label1.Click, AddressOf label1_Click

            panel1.Controls.Add(label1)

        ElseIf e.Node.Text = "CheckBox" Then
            ' Add some checkboxes to the panel 
            checkBox1 = New CheckBox()
            checkBox1.Text = "I am sharp"
            checkBox1.Location = New Point(10, 50)
            AddHandler checkBox1.CheckedChanged, AddressOf CheckBox_CheckedChanged

            panel1.Controls.Add(checkBox1)

            checkBox2 = New CheckBox()
            checkBox2.Text = "I am modest"
            checkBox2.Location = New Point(10, 70)
            AddHandler checkBox2.CheckedChanged, AddressOf CheckBox_CheckedChanged

            panel1.Controls.Add(checkBox2)

        ElseIf e.Node.Text = "RadioButton" Then
            ' Add some radio buttons to the panel
            radiobutton1 = New RadioButton()
            radiobutton1.Text = "I am sharp"
            radiobutton1.Location = New Point(370, 210)
            AddHandler radiobutton1.CheckedChanged, _
                  AddressOf RadioButton_CheckedChanged

            panel1.Controls.Add(radiobutton1)

            radioButton2 = New RadioButton()
            radioButton2.Text = "I am dim-witted"
            radioButton2.Location = New Point(370, 230)
            AddHandler radiobutton1.CheckedChanged, _
                  AddressOf RadioButton_CheckedChanged

            panel1.Controls.Add(radioButton2)

        ElseIf e.Node.Text = "ListBox" Then
            ' Add a listbox to the panel
            listBox1 = New ListBox()
            listBox1.Items.Add("Green")
            listBox1.Items.Add("Beige")
            listBox1.Items.Add("White")
            listBox1.Location = New Point(200, 180)
            AddHandler listBox1.SelectedIndexChanged, _
                  AddressOf listBox1_SelectedIndexChanged

            panel1.Controls.Add(listBox1)

        ElseIf e.Node.Text = "TextBox" Then
            ' Add a text box to the panel
            Dim TextBox1 As TextBox = New TextBox()
            TextBox1.Text = "You can type here"
            TextBox1.Location = New Point(10, 110)

            panel1.Controls.Add(TextBox1)

        ElseIf e.Node.Text = "DataGridView" Then
            ' Add a datagrid, populated with data from an xml file, to the panel
            Dim dataSet1 As DataSet = New DataSet("A sample DataSet")
            dataSet1.ReadXml("../../data/grades.xml")

            Dim dataGridView1 As DataGridView = New DataGridView()
            dataGridView1.Width = Convert.ToInt32((panel1.Width / 2) - 10)
            dataGridView1.Height = 150
            dataGridView1.Location = _
                  New Point(2, panel1.Height - dataGridView1.Height - 5)
            dataGridView1.DataSource = dataSet1
            dataGridView1.DataMember = "subject"

            panel1.Controls.Add(dataGridView1)

        ElseIf e.Node.Text = "TabControl" Then
            ' Add a tab control to the panel 
            ' and add some content to each tab page
            Dim tabControl1 As TabControl = New TabControl()
            tabControl1.Location = New Point(10, 150)
            tabControl1.Size = New Size(165, 146)

            Dim tabPage1 As TabPage = New TabPage("Robynne")
            Dim pictureBox1 As PictureBox = New PictureBox()
            pictureBox1.Image = New Bitmap("../../images/robynne.jpg")
            pictureBox1.Size = New Size(160, 120)
            tabPage1.Controls.Add(pictureBox1)
            tabControl1.TabPages.Add(tabPage1)

            Dim tabPage2 As TabPage = New TabPage("Her Dog")
            Dim pictureBox2 As PictureBox = New PictureBox()
            pictureBox2.Image = New Bitmap("../../images/chocolate.jpg")
            pictureBox2.Size = New Size(160, 120)
            tabPage2.Controls.Add(pictureBox2)
            tabControl1.TabPages.Add(tabPage2)

            Dim tabPage3 As TabPage = New TabPage("Info")
            tabPage3.BackColor = Color.White
            Dim label1 As Label = New Label()
            label1.Text = "Robynne lives in Cape Town, South Africa." _
                & Environment.NewLine & Environment.NewLine _
                & "She has a dog named Chocolate, from the planet Woof," _
                & " rapidly growing into her oversized ears."
            label1.Dock = DockStyle.Fill
            tabPage3.Controls.Add(label1)
            tabControl1.TabPages.Add(tabPage3)

            panel1.Controls.Add(tabControl1)

        ElseIf e.Node.Text = "PictureBox" Then
            ' Add a picture to the panel
            Dim pictureBox1 As PictureBox = New PictureBox()
            pictureBox1.Image = New Bitmap("../../images/ocean.jpg")
            pictureBox1.BorderStyle = BorderStyle.Fixed3D
            pictureBox1.Location = New Point(250, 25)
            pictureBox1.Size = New Size(300, 130)

            panel1.Controls.Add(pictureBox1)

        ElseIf e.Node.Text = "RichTextBox" Then
            ' Add a box for typing rich text in
            ' Load some data from an XML file into it
            Dim richTextBox1 As RichTextBox = New RichTextBox()
            richTextBox1.LoadFile("../../data/grades.xml", _
                  RichTextBoxStreamType.PlainText)
            richTextBox1.WordWrap = False
            richTextBox1.BorderStyle = BorderStyle.Fixed3D
            richTextBox1.BackColor = Color.Beige
            richTextBox1.Size = _
                  New Size(Convert.ToInt32((panel1.Width / 2) - 10), 150)
            richTextBox1.Location = _
                  New Point(Convert.ToInt32((panel1.Width / 2) + 10), _
                  panel1.Height - richTextBox1.Height - 5)

            panel1.Controls.Add(richTextBox1)

        ElseIf e.Node.Text = "MainMenu" Then
            ' Add a classic "menu" (appears at the top of the window)
            Dim mainMenu1 As MainMenu = New MainMenu()

            Dim menuItem1 As MenuItem = New MenuItem("File")
            menuItem1.MenuItems.Add("Exit", _
                  New EventHandler(AddressOf mainMenu1_Exit_Select))
            mainMenu1.MenuItems.Add(menuItem1)
            Dim menuItem2 As MenuItem = New MenuItem("Background")
            menuItem2.MenuItems.Add("Choose", _
                  New EventHandler(AddressOf mainMenu1_ColorOwn_Select))
            menuItem2.MenuItems.Add("White", _
                  New EventHandler(AddressOf mainMenu1_ColorWhite_Select))
            mainMenu1.MenuItems.Add(menuItem2)
            Me.Menu = mainMenu1
            MessageBox.Show("A main menu has been added at the top left of the " _
                  & " window. Try it out after clicking OK.")

        ElseIf e.Node.Text = "ToolBar" Then
            ' Add a shortcuts toolbar to the panel
            Dim toolBar1 As ToolBar = New ToolBar()
            Dim imageList1 As ImageList = New ImageList()
            imageList1.Images.Add(New Bitmap("../../images/open.gif"))
            imageList1.Images.Add(New Bitmap("../../images/close.gif"))
            imageList1.Images.Add(New Bitmap("../../images/undo.gif"))
            toolBar1.ImageList = imageList1

            Dim toolBarbutton1 As ToolBarButton = New ToolBarButton("Open")
            toolBarbutton1.ImageIndex = 0
            toolBar1.Buttons.Add(toolBarbutton1)

            Dim toolBarbutton2 As ToolBarButton = New ToolBarButton("Close")
            toolBarbutton2.ImageIndex = 1
            toolBar1.Buttons.Add(toolBarbutton2)

            Dim toolBarButton3 As ToolBarButton = New ToolBarButton("Huh")
            toolBarButton3.ImageIndex = 3
            toolBar1.Buttons.Add(toolBarButton3)

            AddHandler toolBar1.ButtonClick, AddressOf toolBar1_Click

            panel1.Controls.Add(toolBar1)
        End If
    End Sub

      ' All other event handlers - for the controls added above 
      ' An eventhandler that will be run if the label is clicked
      Private Sub label1_Click(ByVal sender As Object, ByVal e As System.EventArgs)
            MessageBox.Show("Yes, labels can be clicked, " _
                  & "although it's not normal to do so.")
    End Sub

      ' An eventhandler that will be run if the button is clicked
      Private Sub button1_Click(ByVal sender As Object, ByVal e As System.EventArgs)
            MessageBox.Show("Yup, you were supposed to click me")
    End Sub

      ' An eventhandler that will be run if a checkbox is checked/unchecked
      Private Sub CheckBox_CheckedChanged(ByVal sender As Object, _
            ByVal e As System.EventArgs)
            If checkBox1.Checked AndAlso checkBox2.Checked Then
            MessageBox.Show("Good for you")

        ElseIf checkBox1.Checked Then
            MessageBox.Show("It's not good to be sharp without being modest")

        ElseIf checkBox2.Checked Then
            MessageBox.Show("Modesty is good. Pity you're not sharp too.")

            Else
                  MessageBox.Show("Oh dear, neither sharp nor modest eh?")
        End If

    End Sub

      ' An eventhandler that will be run if a radiobutton is clicked
      Private Sub RadioButton_CheckedChanged(ByVal sender As Object, _
            ByVal e As System.EventArgs)
            If radiobutton1.Checked Then
            MessageBox.Show("Glad to hear it")

        ElseIf radioButton2.Checked Then
            MessageBox.Show("What a shame")
        End If
      End Sub

      ' An eventhandler that will be run if an item in the listbox is selected
      Private Sub listBox1_SelectedIndexChanged(ByVal sender As Object, _
            ByVal e As System.EventArgs)
            If listBox1.SelectedItem.ToString() = "Green" Then
            treeView1.BackColor = Color.LightSeaGreen

        ElseIf listBox1.SelectedItem.ToString() = "Beige" Then
            treeView1.BackColor = Color.Beige

        ElseIf listBox1.SelectedItem.ToString() = "White" Then
            treeView1.BackColor = Color.White
            End If
      End Sub

      ' An eventhandler that will be run if "white" is selected at the menu
      Private Sub mainMenu1_ColorWhite_Select(ByVal sender As Object, _
            ByVal e As System.EventArgs)
            treeView1.BackColor = Color.White
      End Sub

      ' An eventhandler that will be run if a color is selected at the menu
      Private Sub mainMenu1_ColorOwn_Select(ByVal sender As Object, _
            ByVal e As System.EventArgs)
            Dim colorDialog1 As ColorDialog = New ColorDialog()
            colorDialog1.Color = treeView1.BackColor
            colorDialog1.ShowDialog()
            treeView1.BackColor = colorDialog1.Color
      End Sub

      ' An eventhandler that will be run if the user chooses "exit" at the menu
      Private Sub mainMenu1_Exit_Select(ByVal sender As Object, _
            ByVal e As System.EventArgs)
        If MessageBox.Show("Are you sure you want to exit?", _
                "Exit confirmation", MessageBoxButtons.YesNo) _
                = Windows.Forms.DialogResult.Yes Then
            Me.Dispose()
        End If
      End Sub

      ' An eventhandler that will be run if a toolbar shortcut is selected
      Private Sub toolBar1_Click(ByVal sender As Object, _
            ByVal e As System.Windows.Forms.ToolBarButtonClickEventArgs)
            If e.Button.Text = "Open" Then
            MessageBox.Show("This could have opened a file, for example")

        ElseIf e.Button.Text = "Close" Then
            MessageBox.Show("This could have closed a file, for example")

        ElseIf e.Button.Text = "Huh" Then
            MessageBox.Show("Huh?")
            End If
      End Sub

    Shared Sub Main()
        ' Start a new instance of a forms application, using our class above
        Application.Run(New FormWithManyControls())
    End Sub

End Class
Bb330919.1f5a9537-844f-4f63-94cd-02e2fc570e4b(en-US,VS.80).png
System.Drawing

Introduction

The classes grouped together in the "Drawing" namespace allow us to work with different types of pictures. On computers, we usually deal with two general types of pictures:

Bitmap or Raster graphics

Vector graphics

Bb330919.a61ceb9e-d624-4d58-b4ff-8b4d79a7b9db(en-US,VS.80).png
Bb330919.1f864ac9-5a7e-416d-a80b-6deac317df1f(en-US,VS.80).png

Bitmap graphics are pictures made up of many dots. For example, photographs and icons can be represented well as bitmaps.

Vector graphics are pictures made up of specific shapes like lines, circles, rectangles, etc. A house plan, for example, can be nicely represented using vector graphics.

Bitmap Graphics

First, we'll show some examples of how to work with bitmap graphics. It is often useful to work with pictures such as photographs on the computer, and the .NET Framework class library includes quite a lot of useful code for doing so.

Example Program 8

This program simply fetches a bitmap image (a JPEG file in this case) from the disk and displays it on a form.

To display an image on a form, it is helpful to use some control that is capable of displaying images. The PictureBox control is perfect for this purpose.

Code for program 8

Imports System
Imports System.Windows.Forms
Imports System.Drawing

Class PictureDisplayer
    Inherits Form

      Private image1 As Bitmap
    Private pictureBox1 As PictureBox

      ' The constructor method for our class
      Public Sub New()
            ' Set the window title and size
            Me.Text = "Picture Displayer"
        Me.Size = New Size(302, 240)

            ' Prepare a box to hold a picture
            pictureBox1 = New PictureBox()
            pictureBox1.SizeMode = PictureBoxSizeMode.StretchImage
            pictureBox1.BorderStyle = BorderStyle.Fixed3D
        pictureBox1.ClientSize = New Size(300, 196)

            ' Add a picture to the box
            image1 = New Bitmap("../../images/lama.jpg")
        pictureBox1.Image = DirectCast(image1, Image)

            ' Add the box (with it's picture) to the form
            Me.Controls.Add(pictureBox1)
    End Sub

    Shared Sub Main()
        ' Start a new instance of a forms application, using our class above
        Application.Run(New PictureDisplayer())
    End Sub
End Class
Bb330919.68488091-620c-4fca-98e8-d9b707629b32(en-US,VS.80).png

Example Program 9

This next program loads a photograph from disk and then also allows the user to flip it horizontally by clicking the "flip" button.

Code for program 9

Imports System
Imports System.Windows.Forms
Imports System.Drawing

Class PictureFlipper
    Inherits Form

      Private button1 As Button
      Private image1 As Bitmap
    Private pictureBox1 As PictureBox

      ' The constructor method for our class
    Public Sub New()

        ' Set the window title and size
        Me.Text = "Picture Flipper"
        Me.Size = New Size(302, 240)

        ' Add a button to the form
        button1 = New Button()
        button1.Text = "Flip"
        button1.Location = New Point(100, 150)
        AddHandler button1.Click, AddressOf button1_Click
        Me.Controls.Add(button1)

        ' Add a picture box to the form
        pictureBox1 = New PictureBox()
        pictureBox1.SizeMode = PictureBoxSizeMode.StretchImage
        pictureBox1.BorderStyle = BorderStyle.Fixed3D
        pictureBox1.ClientSize = New Size(300, 196)

        ' Add an image to the picture box
        image1 = New Bitmap("../../images/elephants.jpg")
        pictureBox1.Image = DirectCast(image1, Image)

        ' Add the picture box (with its image) to the form
        Me.Controls.Add(pictureBox1)
    End Sub

    Shared Sub Main()
        ' Start a new instance of a forms application, using our class above
        Application.Run(New PictureFlipper())
    End Sub

      ' An eventhandler that will run when the button is clicked
    Private Sub button1_Click(ByVal sender As Object, ByVal e As EventArgs)

        ' Flip the image along the X axis (horizontally)
        image1.RotateFlip(RotateFlipType.RotateNoneFlipX)

        ' Re-insert the image into the picture box
        pictureBox1.Image = DirectCast(image1, Image)

        ' Update the window title
        Me.Text = "Picture was flipped"
    End Sub
End Class
Bb330919.faa2acd8-fcca-43d5-aeda-b724f79c4e1b(en-US,VS.80).png
Vector Graphics

Now let's move on to examples dealing with vector graphics - pictures that are made up of specific shapes.

In all of these examples, we'll create a button and an event handler method to catch the button's click event. Only once the button is clicked will we run the code that works with the graphics.

Here are some important concepts to understand. They're very logical - but if you didn't know these you might feel a little confused:

  1. In the real world, to draw a line, circle, rectangle, etc, you first need to select a pen of the correct color and thickness.

    Similarly, to draw a plain shape on the computer, you must first create a Pen object. For example, this code creates a Pen object that will draw in green with a thickness of 3 pixels :

    Dim myGreenPen As Pen = New Pen(Color.Green,3)

  2. To create a colored-in shape, you could use something like a paintbrush.

    On the computer, colored-in shapes can only be created if you have created a Brush object with some chosen color. There are different types of brushes available; the following piece of code will create a blue SolidBrush object :

    Dim myBlueBrush As SolidBrush = New SolidBrush(Color.Blue)

Example Program 10

In this program, the DrawSomeShapes method creates a line, a rectange and an ellipse (a squashed circle).

Code for program 10

Imports System
Imports System.Windows.Forms
Imports System.Drawing

Class SimpleShapeMaker
    Inherits Form

    ' The constructor method for our class
    Public Sub New()

        ' Set the form background to white
        Me.BackColor = Color.White

        ' Add a button, hooked up to an event handler, to the form
        Dim button1 As Button = New Button()
        button1.Text = "click me"
        button1.Location = New Point(110, 10)
        button1.BackColor = Color.SteelBlue
        AddHandler button1.Click, AddressOf button1_Click
        Me.Controls.Add(button1)

    End Sub

      ' An eventhandler that will run when the button is clicked
    Private Sub button1_Click(ByVal o As Object, ByVal e As System.EventArgs)
            ' Execute a specific method we wrote
            DrawSomeShapes()
    End Sub

      ' A method that draws a few shapes on the form surface
    Private Sub DrawSomeShapes()

        '  Prepare a drawing surface for this form
        Dim g As Graphics = Me.CreateGraphics()

        ' Prepare a pen that draws red and with a width of 3 
        Dim redPen As Pen = New Pen(Color.Red, 3)

        ' Use the pen to draw a straight line, a rectangle and an oval
        g.DrawLine(redPen, 140, 170, 140, 230)
        g.DrawRectangle(redPen, 50, 60, 50, 60)
        g.DrawEllipse(redPen, 150, 100, 100, 60)

        ' Clean up
        g.Dispose()
    End Sub

    Shared Sub Main()
        ' Start a new instance of a forms application, using our class above
        Application.Run(New SimpleShapeMaker())
    End Sub

End Class
Bb330919.11320f02-ead5-4d5c-b273-4d98ef05a048(en-US,VS.80).png

Example Program 11

How about we have a bit of fun with the mouse now? Doing interesting graphical things is usually easier with a mouse than with a keyboard. In this next example, we work with both bitmap and vector graphics but also take the opportunity to use a few mouse events.

We do a few interesting new things below - particularly with bitmaps. Although we don’t want to write an essay about it, here’s a little bit of background to help you understand the concepts behind the code:

  • Computer programs make graphics appear on the screen by changing the color and brightness of tiny dots called pixels.

  • Each pixel is made up of the three primary colors: red, green and blue (often shortened to RGB in programming languages). You change the color/brightness of the pixel by varying the strengths of the R, G and B, typically between the values of 0 and 255. For example:

    • if red=255 and green=0 and blue=0, the pixel will appear bright red.

    • if red=255 and green=255 and blue=0, the pixel will appear yellow.

  • The mouse’s position can be detected by the computer and is specified in terms of X and Y co-ordinates (horizontal and vertical co-ordinates). The top left of the screen, for example, is specified by X=0 and Y=0.

Code for program 11

Imports System
Imports System.Windows.Forms
Imports System.Drawing

Class FunWithTheMouse
    Inherits Form

      ' Declare some objects we'll want to talk to from a few methods
      Private pictureBox1 As PictureBox
      Private label1 As Label
    Private spotClicked As Point

      ' The constructor method for our class
    Public Sub New()

        ' Set the window size
        Me.Size = New Size(640, 480)

        ' Load a photo into a picture box and add it to the form
        pictureBox1 = New PictureBox()
        pictureBox1.Image = DirectCast(New Bitmap("../../images/foal.jpg"), Image)
        pictureBox1.SizeMode = PictureBoxSizeMode.Normal
        pictureBox1.Dock = DockStyle.Fill
        Me.Controls.Add(pictureBox1)

        ' Add a label to the bottom, carrying some instructions
        label1 = New Label()
        label1.BackColor = Color.Wheat
        label1.Dock = DockStyle.Bottom
        label1.Text = "Drag rectangle with left mouse button (draw) or another " _
            & "mouse button (lighten). To scribble, hold SHIFT and move mouse."
        label1.TextAlign = ContentAlignment.MiddleCenter
        Me.Controls.Add(label1)

        ' Hook up the picturebox to event handlers for doing mousy things
        AddHandler Me.pictureBox1.MouseDown, AddressOf MouseButtonIsDown
        AddHandler Me.pictureBox1.MouseUp, AddressOf MouseButtonIsUp
        AddHandler Me.pictureBox1.MouseMove, AddressOf TheMouseMoved
    End Sub

      ' An event handler that will run when the mouse is MOVED
    Public Sub TheMouseMoved(ByVal sender As Object, ByVal e As MouseEventArgs)

        ' If the user is holding down a SHIFT key on the keyboard
        If (Control.ModifierKeys And Keys.Shift) = Keys.Shift Then

            ' Prepare a drawing surface on the picture
            Dim g As System.Drawing.Graphics = Me.pictureBox1.CreateGraphics()

            ' Use a yellow pen
            Dim yellowPen As System.Drawing.Pen = _
                  New System.Drawing.Pen(Color.Yellow, 3)

            ' Draw a circle (an ellipse with equal width & height)
            ' at the current X and Y co-ordinates of the mouse
            g.DrawEllipse(yellowPen, e.X, e.Y, 40, 40)

            ' Clean up
            g.Dispose()
        End If
    End Sub

      ' An event handler that will run when a mouse button is pressed DOWN
    Public Sub MouseButtonIsDown(ByVal sender As Object, ByVal e As MouseEventArgs)

        ' Just remember WHERE the mouse was clicked. When the
        ' button is released, we'll want to retrieve this location

        spotClicked.X = e.X ' horizontal co-ordinate
        spotClicked.Y = e.Y ' vertical co-ordinate
    End Sub

      ' An event handler that will run when a mouse button is released
    Public Sub MouseButtonIsUp(ByVal sender As Object, ByVal e As MouseEventArgs)

        ' Ah, the user let go the button they were holding down! 

        ' Define a rectangle (not yet a visual one) that describes
        ' the area of the picture the user wants to do something with
        Dim r As Rectangle = New Rectangle()

        ' The left, top corner is where they pressed the mouse down,
        ' which we "remembered" in the method above
        r.X = spotClicked.X
        r.Y = spotClicked.Y

        ' The width and height of the rectangle can be worked out
        ' by subtracting the original point clicked from where
        ' the mouse is now (when the user is letting go)
        r.Width = e.X - spotClicked.X
        r.Height = e.Y - spotClicked.Y

        If e.Button = Windows.Forms.MouseButtons.Left Then
            ' If left button was pressed/released, just draw 
            ' a visual rectangle so they can see it 

            ' Prepare a drawing surface on the picture box
            Dim g As Graphics = Me.pictureBox1.CreateGraphics()

            ' Draw a rectangle in red
            Dim redPen As Pen = New Pen(Color.Red, 2)
            g.DrawRectangle(redPen, r)
        Else

            '  If it was another button, call our more complicated 
            '  method that knows how to "lighten" an area of the photo
            ChangeLightness(r)
        End If
    End Sub

      ' A method that increases the lightness of the image portion 
      ' selected, by increasing the lightness of each pixel in that area
    Public Sub ChangeLightness(ByVal rect As Rectangle)

        Dim newRed As Integer, newGreen As Integer, newBlue As Integer
        Dim pixel As Color

        ' Get a copy of the picture that's in the picture box
        Dim picture As System.Drawing.Bitmap = New Bitmap(Me.pictureBox1.Image)

        ' Since brightening an area can take a long time,
        ' warn the user about this if they select a big area
        If (rect.Width > 150) OrElse (rect.Height > 150) Then
            Dim result As DialogResult = MessageBox.Show( _
                    "The area you selected is large and may take " _
                    & " a long time to lighten", _
                    "Warning", _
                    MessageBoxButtons.OKCancel)

            ' If they click "cancel", jump out of this method
            ' and return to whatever called it
            If result = Windows.Forms.DialogResult.Cancel Then
                Return
            End If
        End If

        ' Step through all pixels in the given block, doubling the 
        ' brightness of each pixel's RGB (red, green and blue) colors 

        ' From left to right, across the width of the area selected ...
        For x As Integer = rect.X To rect.X + rect.Width - 1

            ' And from top to bottom, down the height of the area selected ...
            For y As Integer = rect.Y To (rect.Y + rect.Height) - 1

                ' Read the pixel we're at
                pixel = picture.GetPixel(x, y)

                ' Prepare a brighter version of the three primary colors in that pixel
                newRed = Convert.ToInt32(Math.Round(pixel.R * 2, 0))
                If newRed > 255 Then
                    newRed = 255
                End If
                newGreen = Convert.ToInt32(Math.Round(pixel.G * 2, 0))
                If newGreen > 255 Then
                    newGreen = 255
                End If
                newBlue = Convert.ToInt32(Math.Round(pixel.B * 2, 0))
                If newBlue > 255 Then
                    newBlue = 255
                End If

                ' Apply the new colors to the pixel
                picture.SetPixel(x, y, _
                                 Color.FromArgb(Convert.ToByte(newRed), _
                                                Convert.ToByte(newGreen), _
                                                Convert.ToByte(newBlue)))
            Next
        Next

        ' Put the modified copy of the picture into the pictureBox 
        ' so the user can see the changes
        Me.pictureBox1.Image = picture
    End Sub

    Shared Sub Main()
        ' Create a new instance of our form class
        Application.Run(New FunWithTheMouse())
    End Sub

End Class
Bb330919.3f5c3780-ee73-4399-8b34-196bad5f783b(en-US,VS.80).png
System.Data

Introduction

Most applications out there need to work with databases. Ask any big company's programmers and you'll hear them speak about how important databases are in the computing world. A programmer who can work with databases will be in a position to create a great many really useful applications.

You might have a database such as Microsoft Access on your computer. Alternatively, you could install Microsoft SQL Server Express Edition, which is a really nice way to learn about the SQL Server database, used in many of the largest companies around the globe. SQL Server Express is available as part of the Visual Basic Express installation, so you may already have it installed.

The System.Data classes in the .NET Framework allow you to work with databases. A database is quite different to things like pictures and word processor documents, which are often called unstructured. A database is more structured. It most often contains many rows of the same type of data, grouped into blocks called tables. The table contains one or more columns and each column holds a particular piece of information for that row.

Rows are sometimes called records and columns are sometimes called fields.

Here is a representation of a database table that holds information about planets. The columns in this case are PlanetName, DistanceFromSun and Inhabitants.

PLANET

PlanetName

DistanceFromSun

Inhabitants

Mercury

57909

Mercurians

Venus

108200

Venusians

Earth

149600

Earthlings

Mars

227940

Martians

Jupiter

778400

Jupiterians

Znock

7208100

Znockers

Saturn

1423600

Saturnians

Uranus

2867000

Uranians

Neptune

4488400

Neptunians

Pluto

5909600

Plutonians

You can see, for example, that the planet Venus is 108 200 thousand kilometers from the sun and that the creatures living there are called Venusians.

Here's another table, this time showing how many creatures were found living on the planets each year.

This is top secret information never revealed before. It was retrieved from an alien craft that crashed in a remote part of the Gobi desert. You should feel privileged to have a copy. Apparently, they too use SQL Server Express databases, which made it easier for us to bundle a copy with the code samples.

POPULATION

PlanetName

Year

Population

Mercury

2000

40000

Venus

2000

25

Earth

2000

6000000000

Mars

2000

325000

Jupiter

2000

8426300200

Znock

2000

550000

Saturn

2000

1000000

Uranus

2000

753425370

Neptune

2000

<NULL>

Pluto

2000

<NULL>

Mercury

2001

35000

Venus

2001

3

Earth

2001

6500000000

Mars

2001

326000

Jupiter

2001

8426300202

Znock

2001

8700

Saturn

2001

75000

Uranus

2001

844360002

Neptune

2001

<NULL>

Pluto

2001

<NULL>

Looking at all the rows that refer to Venus, you'll notice there are two. You can see that in the year 2000 there were 25 Venusians on Venus, but in 2001 there were only 3 of them left. I guess the volcanoes wiped them out.

Don't confuse database tables with spreadsheets. While it's true that spreadsheets can show data in a way that looks like the tables above, the way they work with the data is quite different.

The SQL Language

There are many different databases around the world: Microsoft Access, Oracle, DB2, Microsoft SQL Server, Informix, mySQL and so the list goes on. So how do you talk to a database from Visual Basic? Will they all understand what we're asking for?

The simple answer is that you use a language like Visual Basic to wrap up and send some "database language" to the database, and it decides how to fetch and send back the columns and rows that you asked for.

(To tell the truth, there is another layer in-between called ADO.NET, but we won't talk too much about that here)

Many years ago, because of all the different databases, some people got together and agreed on "one database language" that could speak to most of the databases around. That language is called Structured Query Language (SQL for short). Don’t confuse the SQL language with Microsoft’s product named SQL Server – most databases support the SQL language.

Bb330919.f4937c5d-f14e-48dc-a4f8-d072654eb976(en-US,VS.80).png

Before we talk about how to work with databases in Visual Basic, let's get familiar with the basics of the SQL language. Here follow some examples of statements written in SQL and what happens when you run them.

The three main types of actions are SELECT to view some data, INSERT to insert new data, and UPDATE to change existing data - we'll give examples of each of these.

Usually the way you write Select statements is the following:

SELECT <the Columns you want to see>

FROM <the appropriate Database Tables>

WHERE <some condition is true>

SELECT * 
FROM PLANET

Brings back all rows and all columns from the table called PLANET.

(The star * means all columns)

PlanetName

 DistanceFromSun  

Inhabitants

Mercury

57909

Mercurians

Venus

108200

Venusians

Earth

149600

Earthlings

Mars

227940

Martians

Jupiter

778400

Jupiterians

Znock

7208100

Znockers

Saturn

1423600

Saturnians

Uranus

2867000

Uranians

Neptune

4488400

Neptunians

Pluto

5909600

Plutonians

SELECT PlanetName, Inhabitants 
FROM PLANET

Brings back just the "PlanetName" and "Inhabitants" columns for all rows in the PLANET table.

PlanetName

Inhabitants

Mercury

Mercurians

Venus

Venusians

Earth

Earthlings

Mars

Martians

Jupiter

Jupiterians

Znock

Znockers

Saturn

Saturnians

Uranus

Uranians

Neptune

Neptunians

Pluto

Plutonians

SELECT PlanetName, Inhabitants 
FROM PLANET
WHERE PlanetName='Venus'

Brings back just the "PlanetName" and "Inhabitants" columns for only those rows in the PLANET table which have a PlanetName of "Venus".

PlanetName

Inhabitants

Venus

Venusians

SELECT PlanetName 
FROM POPULATION
WHERE Population<100000

Brings back the PlanetName and Population, from the POPULATION table, wherever the population column has a value less than 100000.

PlanetName

Population

Mercury

40000

Venus

25

Neptune

<NULL>

Pluto

<NULL>

Mercury

35000

Venus

3

Saturn

75000

Neptune

<NULL>

Pluto

<NULL>

Usually the way you write Insert statements is the following:

INSERT INTO <the Database Table you want to add rows to>

(<the Columns you want to add values into>)

INSERT INTO PLANET
      (PlanetName, DistanceFromSun, Inhabitants)
      VALUES 
      ('Fluff', 23500000, 'Fluffies')

Adds a new row to the PLANET table. This is actually a "silent" action - it doesn't bring back any rows to your Visual Basic program - but we show the table here so you get a picture of what's happened.

PLANET

PlanetName

DistanceFromSun

Inhabitants

Mercury

57909

Mercurians

Venus

108200

Venusians

Earth

149600

Earthlings

Mars

227940

Martians

Jupiter

778400

Jupiterians

Znock

7208100

Znockers

Saturn

1423600

Saturnians

Uranus

2867000

Uranians

Neptune

4488400

Neptunians

Pluto

5909600

Plutonians

Fluff

23500000

Fluffies

Usually the way you write Update statements is the following:

UPDATE <the Database Table you want to change>

SET <Columns you want to change> = <new values>

UPDATE PLANET
      SET PlanetName='Stuff', Inhabitants='Stuffies' 
      WHERE PlanetName='Fluff'

Changes some of the values in the row which has a PlanetName "Fluff". We show the resulting table here, but in reality this is a "silent" action and will not bring back any rows to your Visual Basic program.

PLANET

PlanetName

DistanceFromSun  

Inhabitants

Mercury

57909

Mercurians

Venus

108200

Venusians

Earth

149600

Earthlings

Mars

227940

Martians

Jupiter

778400

Jupiterians

Znock

7208100

Znockers

Saturn

1423600

Saturnians

Uranus

2867000

Uranians

Neptune

4488400

Neptunians

Pluto

5909600

Plutonians

Stuff

23500000

Stuffies

Relationships and Joining

If you think about it, you will notice there is a relationship between the two tables PLANET and POPULATION above. They both have a column called "PlanetName." We say that the two tables are related on the column "PlanetName" - and that allows us to collect all the information for a particular planet

We could take, for example, all the rows that have to do with Venus, from both tables ...

PLANET
PlanetName DistanceFromSun   Inhabitants
Venus108200Venusians

POPULATION
PlanetNameYearPopulation
Venus200025
Venus20013

and join them together into what appears to be one big table ...

SELECT * 
FROM PLANET INNER JOIN POPULATION ON PLANET.PlanetName=POPULATION.planetName
WHERE PlanetName='Venus'
PLANETS_AND_POPULATION
PlanetName DistanceFromSun   InhabitantsPlanetNameYearPopulation
Venus108200VenusiansVenus200025
Venus108200VenusiansVenus20013

Which Database are you Using?

There are reasons why programmers may want to do special things for special databases or situations. In the .NET environment, for example, there are several different ways to work with data. If you know you're using a Microsoft SQL Server database, for example, you can use special objects to send your SQL queries and because of that it will work really fast. But if you're talking to Microsoft Access, you can't use that special object.

The code differs slightly then, depending on whether you’re using SQL Server or not, and we’re not sure whether you are. So here’s what we’ve done:

  • The three database example programs in this section (12a, 13a and 14a) are written assuming you have got SQL Server Express installed (or one of the other SQL Server versions).

  • But in case you haven’t, we’ve also included, with the disk samples, a version of each that uses Microsoft Access. These are programs 12b, 13b and 14b, and they will run without needing any database setup at all.

We encourage you to install SQL Server Express at some stage though – it’s a much better database to program against. Additionally, SQL Server skills are more valued in the business world – so the sooner you get to know SQL Server the better. You can download it free from http://msdn.microsoft.com/vstudio/express/sql/download/.

If you have Microsoft SQL Server Express installed and working, use examples 12a, 13a and 14a. If you don’t, or if you have trouble getting them working, you can fall back to examples 12b, 13b and 14b instead, which do the same thing without needing a database installed.

Talking to a Database from Visual Basic

In the following Visual Basic examples, we'll use the SqlConnection and SqlCommand classes to communicate with the SQL Server Express sample database named "Planets". These are the special classes for talking to any version of Microsoft SQL Server. We'll work with the data further in two different ways

  1. Using the SqlDataReader class.

    The SqlDataReader class allows you a lot of programming control since you can step through each data row yourself and choose what to do with the values you get back.

  2. Using the SqlDataAdapter and DataSet classes.

    Datasets are useful if you wish to have the data rows automatically displayed in a forms control such as a datagrid. This approach requires quite a few lines of code to get the data from the database, but saves a lot of trouble in displaying that same data - because smart controls like the DataGridView understand how to hook themselves up to a dataset.

Example Program 12

The following program connects to a SQL Server Express database and sends it a SQL query. It then gets the results back, steps through each row and writes each PlanetName value on a new line in a Label control.

Code for program 12a (SQL Express Version – see disk example 12b for Microsoft Access version)

Imports System
Imports System.Windows.Forms
Imports System.Data
Imports System.Data.SqlClient  ' Namespace for working with SQL Server data

Class SimpleDataAccess
    Inherits Form

    Public Sub New()
        ' Set the window title
        Me.Text = "A simple databasing program"

        ' Determine the physical path to the PLANETS sample database
 Dim dbLocation As String = _
      System.IO.Path.GetFullPath("../../../database/SqlServer/planets.mdf")

        ' Add a label that fills the form
        Dim label1 As Label = New Label()
        label1.Dock = DockStyle.Fill
        Me.Controls.Add(label1)

        ' Connect to the SQL Server database
        Dim connection1 As SqlConnection = New SqlConnection( _
                "data source=.\SQLEXPRESS;" _
                & "User Instance=true;Integrated Security=SSPI;AttachDBFilename=" _
                & dbLocation)

        connection1.Open()

        ' Talk to the database - ask it for data on planets
        Dim sql As String = "SELECT * FROM PLANET"
        Dim command1 As SqlCommand = New SqlCommand(sql, connection1)
        Dim dataReader1 As SqlDataReader = command1.ExecuteReader()

        ' Loop through the records returned and add each planet name to the label
        While dataReader1.Read()
        label1.Text = _
           label1.Text & dataReader1("PlanetName").ToString() & Environment.NewLine
        End While

        ' Clean up
        dataReader1.Close()
        connection1.Close()
    End Sub

    Shared Sub Main()
        ' Start a new instance of a forms application, using our class above
        Application.Run(New SimpleDataAccess())
    End Sub

End Class
Bb330919.274846ec-eea5-4448-8753-f920ed697b01(en-US,VS.80).png

Example Program 13

In this next program we want to display several columns of data, which would be too messy in a Label - so we use a DataGridView.

We execute the same query as the previous program but this time put the results into a DataSet. We then hook the DataGridView to the DataSet and it automatically displays all the data.

Hooking up some invisible back-end data to a visual control is referred to as data binding.

Code for program 13a (SQL Express version – see disk example 13b for Microsoft Access version)

Imports System.Windows.Forms
Imports System.Data
Imports System.Data.SqlClient  ' Namespace for working with SQL Server databases

Class DataInGrid
    Inherits Form

    Public Sub New()
        ' Set the window title
        Me.Text = "One-Way Database Grid Binding"

        ' Determine the physical path to the PLANETS sample database
        Dim dbLocation As String = _
            System.IO.Path.GetFullPath("../../../database/SqlServer/planets.mdf")

        ' Add a DataGridView to the form
        Dim DataGridView1 As DataGridView = New DataGridView()
        DataGridView1.Width = Me.Width
        DataGridView1.Height = 250
        DataGridView1.DataMember = "Table"
        DataGridView1.Dock = DockStyle.Fill
        Me.Controls.Add(DataGridView1)

        ' Connect to the SQL Server database
        Dim connection1 As SqlConnection = New SqlConnection( _
                "data source=.\SQLEXPRESS;" _
                & "User Instance=true;Integrated Security=SSPI;AttachDBFilename=" _
                & dbLocation)
        connection1.Open()

        ' The DataSet will hold the data in memory (in structures called DataTables)
        Dim dataSet1 As DataSet = New DataSet()

        ' The DataAdapter will be the bridge between the database and the dataset
        Dim sqlDataAdapter1 As SqlDataAdapter = New SqlDataAdapter()

        ' Tell the DataAdapter what we want it to fetch, and where from
        sqlDataAdapter1.SelectCommand = New SqlCommand("SELECT * FROM PLANET", connection1)

        ' Fill the in-memory DataSet with the data now
        sqlDataAdapter1.Fill(dataSet1)

        ' Hook the DataGridView (the visual grid) to the in-memory data 
        DataGridView1.DataSource = dataSet1

        ' Close the database connection
        connection1.Close()
    End Sub

    Shared Sub Main()
        ' Start a new instance of a forms application, using our class above
        Application.Run(New DataInGrid())
    End Sub

End Class
Bb330919.05788b30-9bd6-429e-b730-f7c1643e4feb(en-US,VS.80).png

Example Program 14

Displaying data in a DataGridView is okay, but you’ll notice that if you change the data, it does not get saved back into the database. So let’s modify the approach to allow "two-way data binding".

We’ll cheat a little bit here (hey, it’s called "increasing our productivity") by not writing our own UPDATE and INSERT SQL commands – the System.Data namespace has a smart little class called CommandBuilder that can figure out how to write them itself and handles them behind the scenes.

Code for program 14a (SQL Express version – see disk example 14b for Microsoft Access version)

Imports System.Windows.Forms
Imports System.Data
Imports System.Data.SqlClient ' Namespace for working with SQL Server databases

Class PlanetsForm
    Inherits Form

    ' Declare some objects we'll be talking to from different methods
    Private dg As DataGridView
    Private da As SqlDataAdapter

    Public Sub New()
        ' This is the "constructor" method for the PlanetsForm class

        ' Set the window title
        Me.Text = "Two-way Database Grid Binding"

        ' Determine the physical path to the PLANETS sample database
        Dim dbLocation As String = _
               System.IO.Path.GetFullPath("../../../database/SqlServer/planets.mdf")

        ' Prepare to connect to the SQL Server database
        Dim connectionString As String = "data source=.\SQLEXPRESS;" _
                & "User Instance=true;Integrated Security=SSPI;AttachDBFilename=" _
                & dbLocation

        ' Add a "Save" button to the form 
        Dim btnSave As Button = New Button()
        btnSave.Text = "Save"
        AddHandler btnSave.Click, AddressOf BtnSave_Click
        btnSave.Dock = DockStyle.Top
        Me.Controls.Add(btnSave)

        ' Add a DataGridView to the form 
        dg = New DataGridView()
        dg.Width = Me.Width
        dg.Height = 250
        dg.Dock = DockStyle.Fill
        Me.Controls.Add(dg)

        ' Instantiate a few objects that are smart with data and use them 
        ' together to "bind" the DataGridView to the back-end data we want 

        ' DataAdapter will act as bridge between  database and in-memory DataTable
        da = New SqlDataAdapter("SELECT * FROM PLANET", connectionString)

        ' CommandBuilder will handle UPDATE and INSERT automatically
        Dim cb As SqlCommandBuilder = New SqlCommandBuilder(da)

        ' DataTable will keep track, in memory, of changes
        Dim dt As DataTable = New DataTable()

        ' Fill the DataTable with the data now
        da.Fill(dt)

        ' Link the DataTable to the DataGridView now
        dg.DataSource = dt
    End Sub

    Shared Sub Main()
        ' Start a new instance of a forms application, using our class above
        Application.Run(New PlanetsForm())
    End Sub

    Private Sub BtnSave_Click(ByVal sender As Object, ByVal e As System.EventArgs)
        ' Since the save button was clicked, update the database with
        ' any changes made to the DataGridView's underlying source, which
        ' in this case is a DataTable.
        da.Update(DirectCast(dg.DataSource, DataTable))
        MessageBox.Show("Data has been saved", "For your information", MessageBoxButtons.OK)
    End Sub

End Class
Bb330919.a4f1627a-25a2-49b7-a965-74b5125d83ae(en-US,VS.80).png

Try modifying some values and entering new ones. Click "Save" and then close the form. If you re-run the program you will see that the data really has been updated/inserted in the database.

What If I’m Not Using SQL Server Express?

Those of you who do not have a version of Microsoft SQL Server installed, and have a different database you wish to talk to, will need to make a few small adjustments.

First of all, the connection string describing the database location, type, etc. must change.

A connection string for SQL Server Express may look like this:

Dim connectionString As String = _
   "Integrated Security=SSPI;Persist Security Info=False; Initial
   Catalog=Northwind;Data Source=localhost"

or like this, if you’re connecting directly to the database file (as in this book’s examples):

Dim connectionString As String = _
   "data source=.\SQLEXPRESS;Integrated Security=SSPI;
   AttachDBFilename=c:\Visual 
   Basic4#KIDS\examples\database\SqlServer\planets.mdf;
   User Instance=true"

(Because of space we’re wrapping this around to a few lines, but in this format the portion in quotes actually needs to be on one line)

A connection string for Microsoft Access could look like this:

Dim connectionString As String = _
   "Provider=Microsoft.Jet.OLEDB.4.0; Data Source c:\Visual 
   Basic4#KIDS\examples\database\Access\planets.mdb;"

(as explained higher above, you would need to write this on one line)

Other databases will each have a particular format. You may find examples in the Visual Basic Express help documentation or in the documentation that came with your database.

Beyond changing the connection string, you then also change the "Sql" classes to "OleDb" classes.

Start by including System.Data.OleDb namespace instead of the System.Data. SqlClient namespace. This contains classes that can work with a variety of databases.

Imports System.Data.OleDb

Then, swap the classes you use to work with data, as follows:

SQL Server

General Databases

SqlCommand

OleDbCommand

SqlCommandBuilder

OleDbCommandBuilder

SqlDataAdapter

OleDbDataAdapter

SqlConnection

OleDbConnection
System.Xml

Introduction

The classes in System.Xml help you to work with XML data in various ways. Common tasks include:

  • opening an XML document

  • reading a piece of XML to get some specific values out

  • writing an XML file to disk

A Brief Introduction to XML

XML (Extensible Markup Language) is everywhere these days and you're most likely to have heard about it already. XML is a great example of a language that both people and computers can understand. While some computer systems work with data that seems to be a garbled mess to humans, XML is written in plain text and can be read by the average country bumpkin.

You might, for example, put together an XML document like the following to hold some geographical data on disk:

<?xml version="1.0" encoding="utf-8" ?>
 
<Earth>      
             
      <Continent>  
            South America
            <Country capital="Santiago">
                  Chile
            </Country>   
            <Country capital="Buenos Aires">
                  Argentina
            </Country>   
      </Continent>            
             
      <Continent>  
            Asia
            <Country capital="Baghdad">
                  Iraq
            </Country>
             
            <Country capital="New Delhi">
                  India
            </Country>
             
      </Continent>      
</Earth>

Every XML document has this first line simply so programs know there is XML coming

The outermost block

A nested (indented) block with information about the South American continent

More deeply-nested blocks with information about two countries on the Asian continent

It's a lot like HTML, but you're free to make up your own tag names in XML.

Let's talk about two terms you'll need to understand if you're going to read further about XML.

Elements

XML data is held inside elements. An element has a name and usually holds a value. In the example below, the element "Country" has the value "Argentina".

elementname

elementvalue

 

<Country>

Argentina

</Country>

As you can see above, an element is represented with an opening tag and a closing tag. The closing tag must be named exactly like the opening tag, but must include a forward slash "/".

If the element has no value, it is legal to rather use just one tag and close it immediately.

elementname

<Country />

Attributes

But we may want to describe various special things about an element. We may, for example, want to indicate that a country has a capital city - so, as an example, we may create an attribute of our element called "capital". In the example below, the "capital" attribute of the "Country" element "Argentina" is equal to "Buenos Aires".

elementname

 

attributename

 

attributevalue

 

elementvalue

 

<Country

 

capital

=

"Buenos Aires"

>

Argentina

</Country>

All this is quite easy for us humans to read and, since there's a clear structure to it, you can imagine that computers can easily be taught to read it too. "Computer, walk through this document, when you get to a "<" you know you're about to read an element name. When you reach the next ">" then you know to look for the element's value ... and so on.

Example Program 15

The following program reads some geographical data in from an XML file and displays it on a form.

It uses three classes from the System.Xml namespace:

  • XmlDocument (creates an object that can load XML data so we can work with it)

  • XmlNodeList (useful for holding the list of elements we read from the file)

  • XmlNode (holds one XML element)

It allows the user to type in something called an xPath expression to say what elements to get from the xml file. An xPath expression such as //earth/continent/country means "find all elements named "country" wherever they appear beneath an element named "continent" appearing under an element named "earth".

Code for program 15

Imports System
Imports System.Windows.Forms
Imports System.Drawing
Imports System.Xml  ' Namespace for working with XML generally
Imports System.Xml.XPath  ' Namespace for working with XML "paths"

Class XmlRetriever
    Inherits Form

    Private comboBox1 As ComboBox
    Private button1 As Button
    Private listBox1 As ListBox
    Private richTextBox1 As RichTextBox
    Private xmlDoc As XmlDocument

    ' Constructor method for our class
    Public Sub New()

        ' Set the window title and height
        Me.Text = "XML Retrieval"
        Me.Size = New Size(400, 400)

        ' Load an XML file from disk into an XmlDocument object in memory
        xmlDoc = New XmlDocument()
        xmlDoc.Load("../../data/earthData.xml")

        ' Prepare a large text box to show the data in
        richTextBox1 = New RichTextBox()
        richTextBox1.Dock = DockStyle.Top
        richTextBox1.AcceptsTab = True
        richTextBox1.Height = 180
        richTextBox1.[ReadOnly] = True
        richTextBox1.BackColor = Color.Silver

        ' Put the XML into the text box and add the textbox to the form
        richTextBox1.Text = xmlDoc.OuterXml
        Me.Controls.Add(richTextBox1)

        ' Add a combobox control that allows the user to either type
        ' an Xpath expression or to choose an existing one. Add some
        ' as examples to help the user learn to write XPath expressions.
        ' (A combo box is a combination of a textbox and a listbox)
        comboBox1 = New ComboBox()
        comboBox1.Location = New Point(0, 200)
        comboBox1.Width = 300
        comboBox1.Items.Add("//Earth/Continent")
        comboBox1.Items.Add("//Earth/Continent/Country")
        comboBox1.Items.Add("//Earth/Continent/Country[@capital='Nairobi']")
        comboBox1.SelectedIndex = 0
        Me.Controls.Add(comboBox1)

        ' Add a button that will cause the matching items to be displayed
        button1 = New Button()
        button1.Text = "Get data"
        button1.Location = New Point(310, 200)
        AddHandler button1.Click, AddressOf Button1_Click
        Me.Controls.Add(button1)

        ' Add a listbox to display the items returned
        listBox1 = New ListBox()
        listBox1.Dock = DockStyle.Bottom
        listBox1.Location = New Point(10, 10)
        Me.Controls.Add(listBox1)
    End Sub

    Shared Sub Main()
        ' Start a new instance of a forms application, using our class above
        Application.Run(New XmlRetriever())
    End Sub

    ' An eventhandler that will run when the button is clicked
    Private Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs)

        Dim xmlNodes As XmlNodeList
        Dim xmlElement As XmlNode
        Dim elementValue As String

        ' Use a try-catch structure to catch and handle any XPath errors 
        ' neatly instead of just letting the program crash
        Try
            ' From the XML document, select the items specified by the
            ' XPath query chosen in the combobox
            xmlNodes = xmlDoc.SelectNodes(comboBox1.Text)
            listBox1.Items.Clear()

            ' Loop through all the macthing items that were found, 
            ' adding each item to the listbox
            For i As Integer = 0 To xmlNodes.Count - 1
                xmlElement = xmlNodes(i)
                If xmlElement.HasChildNodes Then
                    elementValue = xmlElement.FirstChild.Value.Trim()
                    listBox1.Items.Add(elementValue)
                End If
            Next

        Catch ex As XPathException
            ' If an XPath error was encountered, tell the user neatly and carry on
            MessageBox.Show("No matching data was found. Try another xPath    expression.", _ 
                            "Error Encountered. " + ex.Message)
        End Try
    End Sub

End Class

The program shows the raw xml file in a "RichTextBox" control. Then, below the xPath expression which the user can modify, the resulting element values are shown. So once you get this program running, try changing the expression and clicking the "Get data" button.

Bb330919.94af7ce8-7ac8-4dc0-ac21-7761cdc0076a(en-US,VS.80).png
Page view tracker