Overview of Using Controls in Windows Forms

 

This topic describes the essential elements of a Windows Forms application and provides a simple example that uses controls and handles events in a Windows Forms application.

At a minimum, a Windows Forms application consists of the following elements:

  • One or more classes that derive from System.Windows.Forms.Form.

  • A Main method that invokes the static (shared in Visual Basic) Run method and passes a Form instance to it. The Run method processes messages from the operating system to the application.

The following code example shows the essential elements of a Windows Forms application.

Option Explicit  
Option Strict  
  
Imports System  
Imports System.Windows.Forms  
  
Public Class MyForm  
   Inherits Form  
  
   Public Sub New()  
      Me.Text = "Hello World"  
   End Sub 'New  
  
   <STAThread()> _  
   Public Shared Sub Main()  
      Dim aform As New MyForm()  
      ' The Application.Run method processes messages from the operating system   
      ' to your application. If you comment out the next line of code,   
      ' your application will compile and execute, but because it is not in the  
      ' message loop, it will exit after an instance of the form is created.  
      Application.Run(aform)  
   End Sub  
End Class  

The following code example shows a simple application that illustrates how Windows Forms applications use controls and handle events. The example consists of three buttons on a form; each button changes the background color when clicked.

Option Explicit  
Option Strict  
  
Imports System  
Imports System.ComponentModel  
Imports System.Windows.Forms  
Imports System.Resources  
Imports System.Drawing  
  
Public Class MyForm  
   Inherits Form  
   Private red As Button  
   Private blue As Button  
   Private green As Button  
  
   Public Sub New()  
      InitializeComponent()  
   End Sub  
  
   Protected Overloads Overrides Sub Dispose(disposing as Boolean)  
      MyBase.Dispose(disposing)  
   End Sub  
  
   ' InitializeComponent is a helper method for the constructor.   
   ' It is included for consistency with code that is   
   ' auto-generated by the Windows Forms designer in Visual Studio.   
   Private Sub InitializeComponent()  
  
      ' Creates three buttons, sets their properties, and attaches  
      ' an event handler to each button.  
      red = New Button()  
      red.Text = "Red"  
      red.Location = New Point(100, 50)  
      red.Size = New Size(50, 50)  
      AddHandler red.Click, AddressOf button_Click  
      Controls.Add(red)  
  
      blue = New Button()  
      blue.Text = "Blue"  
      blue.Location = New Point(100, 100)  
      blue.Size = New Size(50, 50)  
      AddHandler blue.Click, AddressOf button_Click  
      Controls.Add(blue)  
  
      green = New Button()  
      green.Text = "Green"  
      green.Location = New Point(100, 150)  
      green.Size = New Size(50, 50)  
      AddHandler green.Click, AddressOf button_Click  
      Controls.Add(green)  
   End Sub  
  
   ' Event handler.  
   Private Sub button_Click(sender As Object, e As EventArgs)  
      If sender Is red Then  
         Me.BackColor = Color.Red  
      Else  
         If sender Is blue Then  
            Me.BackColor = Color.Blue  
         Else  
            Me.BackColor = Color.Green  
         End If  
      End If   
   End Sub  
  
   ' The STAThreadAttribute informs the common language runtime that  
   ' Windows Forms uses the single-threaded apartment model.  
   <STAThread()> _  
   Public Shared Sub Main()  
      Application.Run(New MyForm())  
   End Sub  
End Class  

Developing Custom Windows Forms Controls with the .NET Framework
Windows Forms Control Development Basics

Show: