Use the SaveControlState method to save state information required for the operation of a specific control. This control-state data is stored separately from the control's view-state data.

Custom controls using control state must call the RegisterRequiresControlState method on the Page before saving control state.

When control state is saved, a string object is returned to the client as a variable that is stored in an HTML HIDDEN element. Override this method to extract the state information to use in your control.

Control state is intended for small amounts of critical data, such as a page index or a keyword. Using control state for large amounts of data can adversely affect page performance. For more information, see ASP.NET State Management Overview.

The following code example overrides the SaveControlState method in a custom ASP.NET control. When this method is invoked, it determines whether the internal property currentIndex is set to a non-default value and, if so, saves the value to control state.

The OnInit method is overridden to call the RegisterRequiresControlState method on the Page to indicate that the custom control uses control state.

Class Sample
  Inherits Control

  Dim currentIndex As Integer

      Protected Overrides Sub OnInit(ByVal e As EventArgs)
          Page.RegisterRequiresControlState(Me)
          currentIndex = 0
          MyBase.OnInit(e)
      End Sub

      Protected Overrides Function SaveControlState() As Object
          If currentIndex <> 0 Then
              Return CType(currentIndex, Object)
          Else
              Return Nothing
          End If
      End Function

      Protected Overrides Sub LoadControlState(ByVal state As Object)
          If (state <> Nothing) Then
              currentIndex = CType(state, Integer)
          End If
      End Sub

End Class

public class Sample : Control {
    private int currentIndex = 0;

    protected override void OnInit(EventArgs e) {
        Page.RegisterRequiresControlState(this);
        base.OnInit(e);
    }

    protected override object SaveControlState() {
        return currentIndex != 0 ? (object)currentIndex : null;
    }

    protected override void LoadControlState(object state) {
        if (state != null) {
            currentIndex = (int)state;
        }
    }
}

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

.NET Framework

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