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Control.ClearChildViewState Method

Deletes the view-state information for all the server control's child controls.

[Visual Basic]
Protected Sub ClearChildViewState()
[C#]
protected void ClearChildViewState();
[C++]
protected: void ClearChildViewState();
[JScript]
protected function ClearChildViewState();

Remarks

This method is commonly used when you override the DataBind method when developing templated data-bound server controls. If you do not call this method, child control view-state information can be written to a parent server control, only to be overridden when data binding occurs.

For more information about using this method, see Developing a Templated Data-Bound Control.

Example

The following example demonstrates how to override the OnDataBinding method for a templated data-bound control. If the DataSource that the control binds to is populated, the control's ControlCollection is emptied, using the Controls.Clear method, and the ClearChildViewState method is used to remove any view-state information that had been saved for the child controls.

[Visual Basic] 
' Override to create the repeated items from the DataSource.
Protected Overrides Sub OnDataBinding(E As EventArgs)
    MyBase.OnDataBinding(e)

    If Not DataSource Is Nothing
        ' Clear any existing child controls.
        Controls.Clear()
        ' Clear any previous view state for the existing child controls.
        ClearChildViewState()

        ' Iterate over the DataSource, creating a new item for each data item.
        Dim DataEnum As IEnumerator = DataSource.GetEnumerator()
        Dim I As Integer = 0
        Do While (DataEnum.MoveNext())

            ' Create an item.
            Dim Item As RepeaterItemVB = New RepeaterItemVB(I, DataEnum.Current)
            ' Initialize the item from the template.
            ItemTemplate.InstantiateIn(Item)
            ' Add the item to the ControlCollection.
            Controls.Add(Item)

            I = I + 1
        Loop

        ' Prevent child controls from being created again.
        ChildControlsCreated = true
        ' Store the number of items created in view state for postback scenarios.
        ViewState("NumItems") = I
    End If
End Sub

[C#] 
// Override to create the repeated items from the DataSource.
protected override void OnDataBinding(EventArgs e) {
    base.OnDataBinding(e);

    if (DataSource != null) {
        // Clear any existing child controls.
        Controls.Clear();
        // Clear any previous view state for the existing child controls.
        ClearChildViewState();

        // Iterate over the DataSource, creating a new item for each data item.
        IEnumerator dataEnum = DataSource.GetEnumerator();
        int i = 0;
        while(dataEnum.MoveNext()) {

            // Create an item.
            RepeaterItem item = new RepeaterItem(i, dataEnum.Current);
            // Initialize the item from the template.
            ItemTemplate.InstantiateIn(item);
            // Add the item to the ControlCollection.
            Controls.Add(item);

            i++;
        }

        // Prevent child controls from being created again.
        ChildControlsCreated = true;
        // Store the number of items created in view state for postback scenarios.
        ViewState["NumItems"] = i;
    }
}

[C++] 
// Override to create the repeated items from the DataSource.
protected:
void OnDataBinding(EventArgs * e) 
{
   __super::OnDataBinding(e);

   if (DataSource != 0) 
   {
      // Clear any existing child controls.
      Controls->Clear();
      // Clear any previous view state for the existing child controls.
      ClearChildViewState();

      // Iterate over the DataSource, creating a new item for each data item.
      IEnumerator* dataEnum = DataSource->GetEnumerator();
      int i = 0;
      while(dataEnum->MoveNext()) 
      {
         // Create an item.
         RepeaterItem* item = new RepeaterItem(i, dataEnum->Current);
         // Initialize the item from the template.
         ItemTemplate->InstantiateIn(item);
         // Add the item to the ControlCollection.
         Controls->Add(item);
         i++;
      }

      // Prevent child controls from being created again.
      ChildControlsCreated = true;
      // Store the number of items created in view state for postback scenarios.
      ViewState->Item[S"NumItems"] = __box(i);
   }
}

[JScript] 
// Override to create the repeated items from the DataSource.
protected override function OnDataBinding(e : EventArgs) {
    super.OnDataBinding(e);

    if (DataSource != null) {
        // Clear any existing child controls.
        Controls.Clear();
        // Clear any previous view state for the existing child controls.
        ClearChildViewState();

        // Iterate over the DataSource, creating a new item for each data item.
        var dataEnum : IEnumerator = DataSource.GetEnumerator();
        var i : int = 0;
        while(dataEnum.MoveNext()) {

            // Create an item.
            var item : RepeaterItem = new RepeaterItem(i, dataEnum.Current);
            // Initialize the item from the template.
            ItemTemplate.InstantiateIn(item);
            // Add the item to the ControlCollection.
            Controls.Add(item);

            i++;
        }

        // Prevent child controls from being created again.
        ChildControlsCreated = true;
        // Store the number of items created in view state for postback scenarios.
        ViewState["NumItems"] = i;
    }
}

Requirements

Platforms: Windows 2000, Windows XP Professional, Windows Server 2003 family

See Also

Control Class | Control Members | System.Web.UI Namespace | ViewState | DataBind | Developing a Templated Data-Bound Control

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