Invokes the default window procedure associated with this window.
Assembly: System.Windows.Forms (in System.Windows.Forms.dll)
The following code example demonstrates intercepting operating system window messages in a window procedure. The example creates a class that inherits from NativeWindow to accomplish this.
The MyNativeWindowListener class hooks into the window procedure of the form passed into the constructor, and overrides the method to intercept the WM_ACTIVATEAPP window message. The class demonstrates the use of the AssignHandle and ReleaseHandle methods to identify the window handle the NativeWindow will use. The handle is assigned based upon the Control.HandleCreated and Control.HandleDestroyed events. When the WM_ACTIVATEAPP window message is received, the class calls the form1 ApplicationActivated method.
' NativeWindow class to listen to operating system messages. Friend Class MyNativeWindowListener Inherits NativeWindow ' Constant value was found in the "windows.h" header file. Private Const WM_ACTIVATEAPP As Integer = &H1C Private parent As Form1 Public Sub New(ByVal parent As Form1) AddHandler parent.HandleCreated, AddressOf Me.OnHandleCreated AddHandler parent.HandleDestroyed, AddressOf Me.OnHandleDestroyed Me.parent = parent End Sub ' Listen for the control's window creation and hook into it. Private Sub OnHandleCreated(ByVal sender As Object, ByVal e As EventArgs) ' Window is now created, assign handle to NativeWindow. AssignHandle(CType(sender, Form).Handle) End Sub Private Sub OnHandleDestroyed(ByVal sender As Object, ByVal e As EventArgs) ' Window was destroyed, release hook. ReleaseHandle() End Sub <System.Security.Permissions.PermissionSetAttribute(System.Security.Permissions.SecurityAction.Demand, Name:="FullTrust")> _ Protected Overrides Sub WndProc(ByRef m As Message) ' Listen for operating system messages Select Case (m.Msg) Case WM_ACTIVATEAPP ' Notify the form that this message was received. ' Application is activated or deactivated, ' based upon the WParam parameter. parent.ApplicationActivated(m.WParam.ToInt32() <> 0) End Select MyBase.WndProc(m) End Sub End Class
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
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.