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
Declare an integer variable to store the child list position and a Boolean variable to store whether to cache the child position.
private int cachedPosition = -1; private bool cacheChildPosition = true;Private cachedPosition As Integer = - 1 Private cacheChildPosition As Boolean = TrueHandle the ListChanged event for the binding's CurrencyManager and check for a ListChangedType of Reset.
Check the current position of the CurrencyManager. If it is greater than first entry in the list (typically 0), save it to a variable.
void relatedCM_ListChanged(object sender, ListChangedEventArgs e) { // Check to see if this is a caching situation. if (cacheChildPosition && cachePositionCheckBox.Checked) { // If so, check to see if it is a reset situation, and the current // position is greater than zero. CurrencyManager relatedCM = sender as CurrencyManager; if (e.ListChangedType == ListChangedType.Reset && relatedCM.Position > 0) // If so, cache the position of the child table. cachedPosition = relatedCM.Position; } }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 SubHandle 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.
void bindingSource1_CurrentChanged(object sender, EventArgs e) { // If the CurrentChanged event occurs, this is not a caching // situation. cacheChildPosition = false; }' 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
Handle the PositionChanged event for the child binding's CurrencyManager.
Reset the child table position to the cached position saved in the previous procedure.
void relatedCM_PositionChanged(object sender, EventArgs e) { // Check to see if this is a caching situation. if (cacheChildPosition && cachePositionCheckBox.Checked) { CurrencyManager relatedCM = sender as CurrencyManager; // 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 && cachedPosition > 0 && cachedPosition < relatedCM.Count) { relatedCM.Position = cachedPosition; cachedPosition = -1; } } }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
Example
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.
using System;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
namespace BT2
{
public class Form1 : Form
{
public Form1()
{
InitializeControlsAndDataSource();
}
// Declare the controls to be used.
private BindingSource bindingSource1;
private DataGridView dataGridView1;
private Button button1;
private DataGridView dataGridView2;
private CheckBox cachePositionCheckBox;
public DataSet set1;
private void InitializeControlsAndDataSource()
{
// Initialize the controls and set location, size and
// other basic properties.
this.dataGridView1 = new DataGridView();
this.bindingSource1 = new BindingSource();
this.button1 = new Button();
this.dataGridView2 = new DataGridView();
this.cachePositionCheckBox = new System.Windows.Forms.CheckBox();
this.dataGridView1.ColumnHeadersHeightSizeMode =
DataGridViewColumnHeadersHeightSizeMode.AutoSize;
this.dataGridView1.Dock = DockStyle.Top;
this.dataGridView1.Location = new Point(0, 20);
this.dataGridView1.Size = new Size(292, 170);
this.button1.Location = new System.Drawing.Point(18, 175);
this.button1.Size = new System.Drawing.Size(125, 23);
button1.Text = "Clear Parent Field";
this.button1.Click += new System.EventHandler(this.button1_Click);
this.dataGridView2.ColumnHeadersHeightSizeMode =
System.Windows.Forms.DataGridViewColumnHeadersHeightSizeMode.AutoSize;
this.dataGridView2.Location = new System.Drawing.Point(0, 225);
this.dataGridView2.Size = new System.Drawing.Size(309, 130);
this.cachePositionCheckBox.AutoSize = true;
this.cachePositionCheckBox.Checked = true;
this.cachePositionCheckBox.Location = new System.Drawing.Point(150, 175);
this.cachePositionCheckBox.Name = "radioButton1";
this.cachePositionCheckBox.Size = new System.Drawing.Size(151, 17);
this.cachePositionCheckBox.Text = "Cache and restore position";
this.ClientSize = new System.Drawing.Size(325, 420);
this.Controls.Add(this.dataGridView1);
this.Controls.Add(this.cachePositionCheckBox);
this.Controls.Add(this.dataGridView2);
this.Controls.Add(this.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.
CurrencyManager relatedCM =
bindingSource1.GetRelatedCurrencyManager("custOrders");
// Set the position in the child table for demonstration purposes.
relatedCM.Position = 3;
// 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.
bindingSource1.CurrentChanged +=
new EventHandler(bindingSource1_CurrentChanged);
// Handle the two events for caching and resetting the position.
relatedCM.ListChanged += new ListChangedEventHandler(relatedCM_ListChanged);
relatedCM.PositionChanged
+= new EventHandler(relatedCM_PositionChanged);
// Set cacheing to true in case current changed event
// occurred on set up.
cacheChildPosition = true;
}
// Establish the data set with two tables and a relationship
// between them.
private DataSet InitializeDataSet()
{
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");
DataRelation dr = new DataRelation("custOrders",
set1.Tables["Customers"].Columns["CustomerID"],
set1.Tables["Orders"].Columns["CustomerID"]);
set1.Relations.Add(dr);
return set1;
}
private int cachedPosition = -1;
private bool cacheChildPosition = true;
void relatedCM_ListChanged(object sender, ListChangedEventArgs e)
{
// Check to see if this is a caching situation.
if (cacheChildPosition && cachePositionCheckBox.Checked)
{
// If so, check to see if it is a reset situation, and the current
// position is greater than zero.
CurrencyManager relatedCM = sender as CurrencyManager;
if (e.ListChangedType == ListChangedType.Reset && relatedCM.Position > 0)
// If so, cache the position of the child table.
cachedPosition = relatedCM.Position;
}
}
void bindingSource1_CurrentChanged(object sender, EventArgs e)
{
// If the CurrentChanged event occurs, this is not a caching
// situation.
cacheChildPosition = false;
}
void relatedCM_PositionChanged(object sender, EventArgs e)
{
// Check to see if this is a caching situation.
if (cacheChildPosition && cachePositionCheckBox.Checked)
{
CurrencyManager relatedCM = sender as CurrencyManager;
// 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 && cachedPosition
> 0 && cachedPosition < relatedCM.Count)
{
relatedCM.Position = cachedPosition;
cachedPosition = -1;
}
}
}
int count = 0;
private void button1_Click(object sender, EventArgs e)
{
// For demo purposes--modifies a value in the first row of the
// parent table.
DataRow row1 = set1.Tables[0].Rows[0];
row1[1] = DBNull.Value;
}
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Form1());
}
}
}
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
' occurred on set up.
cacheChildPosition = True
End Sub
' 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:
Run the example.
Make sure the Cache and reset position check box is selected.
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.
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.
Clear the Cache and reset position check box.
Click the Clear parent field button. Notice that the selected row in the child table changes to the first row.
Compiling the Code
This example requires:
- References to the System, System.Data, System.Drawing, System.Windows.Forms, and System.XML assemblies.
See also
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