How to: Ensure the Selected Row in a Child Table Remains at the Correct Position

Oftentimes when you work with data binding in Windows Forms, you will display data in what is called a parent/child or master/details view. This refers to a data-binding scenario where data from the same source is displayed in two controls. Changing the selection in one control causes the data displayed in the second control to change. For example, the first control might contain a list of customers and the second a list of orders related to the selected customer in the first control.

Starting with the .NET Framework version 2.0, when you display data in a parent/child view you might have to take extra steps to make sure that the currently selected row in the child table is not reset to the first row of the table. In order to do this, you will have to cache the child table position and reset it after the parent table changes. Typically the child reset occurs the first time a field in a row of the parent table changes.

To Cache the Current Child Position

  1. Declare an integer variable to store the child list position and a Boolean variable to store whether to cache the child position.

    Private cachedPosition As Integer = - 1
    Private cacheChildPosition As Boolean = True
    
  2. Handle the ListChanged event for the binding's CurrencyManager and check for a ListChangedType of Reset.

  3. Check the current position of the CurrencyManager. If it is greater than first entry in the list (typically 0), save it to a variable.

    Private Sub relatedCM_ListChanged(ByVal sender As Object, _
        ByVal e As ListChangedEventArgs)
        ' Check to see if this is a caching situation. 
        If cacheChildPosition AndAlso cachePositionCheckBox.Checked Then 
            ' If so, check to see if it is a reset situation, and the current 
            ' position is greater than zero. 
            Dim relatedCM As CurrencyManager = sender
            If e.ListChangedType = ListChangedType.Reset _
                AndAlso relatedCM.Position > 0 Then 
    
                ' If so, cache the position of the child table.
                cachedPosition = relatedCM.Position
            End If 
        End If 
    
    End Sub
    
  4. Handle the parent list's CurrentChanged event for the parent currency manager. In the handler, set the Boolean value to indicate it is not a caching scenario. If the CurrentChanged occurs, the change to the parent is a list position change and not an item value change.

    ' Handle the current changed event. This event occurs when 
    ' the current item is changed, but not when a field of the current 
    ' item is changed. 
    Private Sub bindingSource1_CurrentChanged(ByVal sender As Object, _
        ByVal e As EventArgs) Handles bindingSource1.CurrentChanged
        ' If the CurrentChanged event occurs, this is not a caching  
        ' situation.
        cacheChildPosition = False 
    
    End Sub
    

To Reset the Child Position

  1. Handle the PositionChanged event for the child binding's CurrencyManager.

  2. Reset the child table position to the cached position saved in the previous procedure.

    Private Sub relatedCM_PositionChanged(ByVal sender As Object, ByVal e As EventArgs) 
        ' Check to see if this is a caching situation. 
        If cacheChildPosition AndAlso cachePositionCheckBox.Checked Then 
            Dim relatedCM As CurrencyManager = sender
    
            ' If so, check to see if the current position is  
            ' not equal to the cached position and the cached  
            ' position is not out of bounds. 
            If relatedCM.Position <> cachedPosition AndAlso _
                cachedPosition > 0 AndAlso cachedPosition < _
                relatedCM.Count Then
                relatedCM.Position = cachedPosition
                cachedPosition = -1
            End If 
        End If 
    End Sub
    

The following example demonstrates how to save the current position on the CurrencyManager.for a child table and reset the position after an edit is completed on the parent table. This example contains two DataGridView controls bound to two tables in a DataSet using a BindingSource component. A relation is established between the two tables and the relation is added to the DataSet. The position in the child table is initially set to the third row for demonstration purposes.

Imports System
Imports System.ComponentModel
Imports System.Data
Imports System.Drawing
Imports System.Text
Imports System.Windows.Forms



Public Class Form1
    Inherits Form

    Public Sub New() 
        InitializeControlsAndDataSource()

    End Sub 

    ' Declare the controls to be used. 
    Private WithEvents bindingSource1 As BindingSource
    Private dataGridView1 As DataGridView
    Private WithEvents button1 As Button
    Private dataGridView2 As DataGridView
    Private cachePositionCheckBox As CheckBox
    Public set1 As DataSet


    Private Sub InitializeControlsAndDataSource() 
        ' Initialize the controls and set location, size and  
        ' other basic properties. 
        Me.dataGridView1 = New DataGridView()
        Me.bindingSource1 = New BindingSource()
        Me.button1 = New Button()
        Me.dataGridView2 = New DataGridView()
        Me.cachePositionCheckBox = New System.Windows.Forms.CheckBox()
        Me.dataGridView1.ColumnHeadersHeightSizeMode = _
            DataGridViewColumnHeadersHeightSizeMode.AutoSize
        Me.dataGridView1.Dock = DockStyle.Top
        Me.dataGridView1.Location = New Point(0, 20)
        Me.dataGridView1.Size = New Size(292, 170)
        Me.button1.Location = New System.Drawing.Point(18, 175)
        Me.button1.Size = New System.Drawing.Size(125, 23)

        button1.Text = "Clear Parent Field" 

        Me.dataGridView2.ColumnHeadersHeightSizeMode = _
            System.Windows.Forms.DataGridViewColumnHeadersHeightSizeMode.AutoSize
        Me.dataGridView2.Location = New System.Drawing.Point(0, 225)
        Me.dataGridView2.Size = New System.Drawing.Size(309, 130)
        Me.cachePositionCheckBox.AutoSize = True 
        Me.cachePositionCheckBox.Checked = True 
        Me.cachePositionCheckBox.Location = New System.Drawing.Point(150, 175)
        Me.cachePositionCheckBox.Name = "radioButton1" 
        Me.cachePositionCheckBox.Size = New System.Drawing.Size(151, 17)
        Me.cachePositionCheckBox.Text = "Cache and restore position" 
        Me.ClientSize = New System.Drawing.Size(325, 420)
        Me.Controls.Add(Me.dataGridView1)
        Me.Controls.Add(Me.cachePositionCheckBox)
        Me.Controls.Add(Me.dataGridView2)
        Me.Controls.Add(Me.button1)

        ' Initialize the data.
        set1 = InitializeDataSet()

        ' Set the data source to the DataSet.
        bindingSource1.DataSource = set1

        'Set the DataMember to the Menu table.
        bindingSource1.DataMember = "Customers" 

        ' Add the control data bindings.
        dataGridView1.DataSource = bindingSource1

        ' Set the data source and member for the second DataGridView.
        dataGridView2.DataSource = bindingSource1
        dataGridView2.DataMember = "custOrders" 

        ' Get the currency manager for the customer orders binding. 
        Dim relatedCM As CurrencyManager = _
            bindingSource1.GetRelatedCurrencyManager("custOrders")

        ' Handle the two events for caching and resetting the position. 
        AddHandler relatedCM.ListChanged, AddressOf relatedCM_ListChanged
        AddHandler relatedCM.PositionChanged, AddressOf relatedCM_PositionChanged

        ' Set the position in the child table for demonstration purposes.
        relatedCM.Position = 3

        ' Set cacheing to true in case current changed event 
        ' occured on set up.
        cacheChildPosition = True 


    End Sub 'InitializeControlsAndDataSource



    ' Establish the data set with two tables and a relationship 
    ' between them. 
    Private Function InitializeDataSet() As DataSet 
        set1 = New DataSet()
        ' Declare the DataSet and add a table and column.
        set1.Tables.Add("Customers")
        set1.Tables(0).Columns.Add("CustomerID")
        set1.Tables(0).Columns.Add("Customer Name")
        set1.Tables(0).Columns.Add("Contact Name")

        ' Add some rows to the table.
        set1.Tables("Customers").Rows.Add("c1", "Fabrikam, Inc.", _
            "Ellen Adams")
        set1.Tables(0).Rows.Add("c2", "Lucerne Publishing", "Don Hall")
        set1.Tables(0).Rows.Add("c3", "Northwind Traders", "Lori Penor")
        set1.Tables(0).Rows.Add("c4", "Tailspin Toys", "Michael Patten")
        set1.Tables(0).Rows.Add("c5", "Woodgrove Bank", "Jyothi Pai")

        ' Declare the DataSet and add a table and column.
        set1.Tables.Add("Orders")
        set1.Tables(1).Columns.Add("CustomerID")
        set1.Tables(1).Columns.Add("OrderNo")
        set1.Tables(1).Columns.Add("OrderDate")

        ' Add some rows to the table.
        set1.Tables(1).Rows.Add("c1", "119", "10/04/2006")
        set1.Tables(1).Rows.Add("c1", "149", "10/10/2006")
        set1.Tables(1).Rows.Add("c1", "159", "10/12/2006")
        set1.Tables(1).Rows.Add("c2", "169", "10/10/2006")
        set1.Tables(1).Rows.Add("c2", "179", "10/10/2006")
        set1.Tables(1).Rows.Add("c2", "189", "10/12/2006")
        set1.Tables(1).Rows.Add("c3", "122", "10/04/2006")
        set1.Tables(1).Rows.Add("c4", "130", "10/10/2006")
        set1.Tables(1).Rows.Add("c5", "1.29", "10/14/2006")

        Dim dr As New DataRelation("custOrders", _
            set1.Tables("Customers").Columns("CustomerID"), _
            set1.Tables("Orders").Columns("CustomerID"))
        set1.Relations.Add(dr)
        Return set1

    End Function '
    Private cachedPosition As Integer = - 1
    Private cacheChildPosition As Boolean = True 

    Private Sub relatedCM_ListChanged(ByVal sender As Object, _
        ByVal e As ListChangedEventArgs)
        ' Check to see if this is a caching situation. 
        If cacheChildPosition AndAlso cachePositionCheckBox.Checked Then 
            ' If so, check to see if it is a reset situation, and the current 
            ' position is greater than zero. 
            Dim relatedCM As CurrencyManager = sender
            If e.ListChangedType = ListChangedType.Reset _
                AndAlso relatedCM.Position > 0 Then 

                ' If so, cache the position of the child table.
                cachedPosition = relatedCM.Position
            End If 
        End If 

    End Sub 

    ' Handle the current changed event. This event occurs when 
    ' the current item is changed, but not when a field of the current 
    ' item is changed. 
    Private Sub bindingSource1_CurrentChanged(ByVal sender As Object, _
        ByVal e As EventArgs) Handles bindingSource1.CurrentChanged
        ' If the CurrentChanged event occurs, this is not a caching  
        ' situation.
        cacheChildPosition = False 

    End Sub 

    Private Sub relatedCM_PositionChanged(ByVal sender As Object, ByVal e As EventArgs) 
        ' Check to see if this is a caching situation. 
        If cacheChildPosition AndAlso cachePositionCheckBox.Checked Then 
            Dim relatedCM As CurrencyManager = sender

            ' If so, check to see if the current position is  
            ' not equal to the cached position and the cached  
            ' position is not out of bounds. 
            If relatedCM.Position <> cachedPosition AndAlso _
                cachedPosition > 0 AndAlso cachedPosition < _
                relatedCM.Count Then
                relatedCM.Position = cachedPosition
                cachedPosition = -1
            End If 
        End If 
    End Sub 

    Private count As Integer = 0

    Private Sub button1_Click(ByVal sender As Object, _
        ByVal e As EventArgs) Handles button1.Click
        ' For demo purposes--modifies a value in the first row of the 
        ' parent table. 
        Dim row1 As DataRow = set1.Tables(0).Rows(0)
        row1(1) = DBNull.Value
    End Sub

    <STAThread()>  _
    Shared Sub Main() 
        Application.EnableVisualStyles()
        Application.SetCompatibleTextRenderingDefault(False)
        Application.Run(New Form1())

    End Sub 
End Class

To test the code example, perform the following steps:

  1. Run the example.

  2. Make sure the Cache and reset position check box is selected.

  3. Click the Clear parent field button to cause a change in a field of the parent table. Notice that the selected row in the child table does not change.

  4. Close and run the example again. You need to do this because the reset behavior occurs only on the first change in the parent row.

  5. Clear the Cache and reset position check box.

  6. Click the Clear parent field button. Notice that the selected row in the child table changes to the first row.

This example requires:

  • References to the System, System.Data, System.Drawing, System.Windows.Forms, and System.XML assemblies.

For information about how to build this example from the command line for Visual Basic or Visual C#, see Building from the Command Line (Visual Basic) or Command-line Building With csc.exe. You can also build this example in Visual Studio by pasting the code into a new project. How to: Compile and Run a Complete Windows Forms Code Example Using Visual Studio
How to: Compile and Run a Complete Windows Forms Code Example Using Visual Studio
How to: Compile and Run a Complete Windows Forms Code Example Using Visual Studio
How to: Compile and Run a Complete Windows Forms Code Example Using Visual Studio
How to: Compile and Run a Complete Windows Forms Code Example Using Visual Studio

Was this page helpful?
(1500 characters remaining)
Thank you for your feedback
Show:
© 2014 Microsoft