The AxHost..::.AboutBoxDelegate provides you the ability to be notified when the ActiveX control's About box is going to be displayed. Code added to the delegate method is executed before the About box is displayed.

When you create an AxHost..::.AboutBoxDelegate delegate, you identify the method that will handle the display of an ActiveX control's About dialog box if it has one. To associate the method with your handler, add an instance of the delegate to the method. The handler is called whenever the method is called, unless you remove the delegate. For more information about delegates, see Events and Delegates.

The following example overrides the constructor, and the SetAboutBoxDelegate and AttachInterfaces methods of an AxHost derived class that wraps the Microsoft Masked Edit ActiveX Control. This code assumes you have created the generated source code by running the AxImp.exe on the MSMask32.ocx file with the /source switch to generate the wrapper class to be edited. This code is only shown in C# syntax as that is the the only language output by the AxImp.exe.

public AxMaskEdBox()
    :
  base("c932ba85-4374-101b-a56c-00aa003668dc") // The ActiveX control's class identifier.
{
    // Make the AboutBox method the about box delegate.
    this.SetAboutBoxDelegate(new AboutBoxDelegate(AboutBox));
}

public virtual void AboutBox()
{
    // If the instance of the ActiveX control is null when the AboutBox method 
    // is called, raise an InvalidActiveXStateException exception.
    if ((this.ocx == null))
    {
        throw new System.Windows.Forms.AxHost.InvalidActiveXStateException(
          "AboutBox", System.Windows.Forms.AxHost.ActiveXInvokeKind.MethodInvoke);
    }
    // Show the about box if the ActiveX control has one.
    if (this.HasAboutBox)
    {
        this.ocx.AboutBox();
    }
}

protected override void AttachInterfaces()
{
    try
    {
        // Attach the IMSMask interface to the ActiveX control.
        this.ocx = ((MSMask.IMSMask)(this.GetOcx()));
    }
    catch (System.Exception ex)
    {
        System.Console.WriteLine(ex.Message);
    }
}

.NET Framework

.NET Framework Client Profile

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference