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NativeWindow.WndProc(Message) Method

  • Reference

Definition

Namespace:
System.Windows.Forms
Assembly:
System.Windows.Forms.dll

Invokes the default window procedure associated with this window.

protected:
 virtual void WndProc(System::Windows::Forms::Message % m);
protected virtual void WndProc (ref System.Windows.Forms.Message m);
abstract member WndProc : Message -> unit
override this.WndProc : Message -> unit
Protected Overridable Sub WndProc (ByRef m As Message)

Parameters

m
Message

A Message that is associated with the current Windows message.

Examples

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 WndProc 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.

This code is an excerpt from the example shown in the NativeWindow class overview. Some code is not shown for the purpose of brevity. See NativeWindow for the whole code listing.

// NativeWindow class to listen to operating system messages.
ref class MyNativeWindowListener: public NativeWindow
{
private:

   // Constant value was found in the S"windows.h" header file.
   literal int WM_ACTIVATEAPP = 0x001C;
   Form1^ parent;

public:
   MyNativeWindowListener( Form1^ parent )
   {
      parent->HandleCreated += gcnew EventHandler( this, &MyNativeWindowListener::OnHandleCreated );
      parent->HandleDestroyed += gcnew EventHandler( this, &MyNativeWindowListener::OnHandleDestroyed );
      this->parent = parent;
   }

internal:

   // Listen for the control's window creation and then hook into it.
   void OnHandleCreated( Object^ sender, EventArgs^ /*e*/ )
   {
      // Window is now created, assign handle to NativeWindow.
      AssignHandle( (dynamic_cast<Form1^>(sender))->Handle );
   }

   void OnHandleDestroyed( Object^ /*sender*/, EventArgs^ /*e*/ )
   {
      // Window was destroyed, release hook.
      ReleaseHandle();
   }

protected:

   virtual void WndProc( Message %m ) override
   {
      // Listen for operating system messages
      switch ( m.Msg )
      {
         case WM_ACTIVATEAPP:

            // Notify the form that this message was received.
            // Application is activated or deactivated,
            // based upon the WParam parameter.
            parent->ApplicationActived( ((int)m.WParam != 0) );
            break;
      }
      NativeWindow::WndProc( m );
   }

};

// NativeWindow class to listen to operating system messages.
internal class MyNativeWindowListener : NativeWindow
{
    // Constant value was found in the "windows.h" header file.
    private const int WM_ACTIVATEAPP = 0x001C;

    private Form1 parent;

    public MyNativeWindowListener(Form1 parent)
    {

        parent.HandleCreated += new EventHandler(this.OnHandleCreated);
        parent.HandleDestroyed += new EventHandler(this.OnHandleDestroyed);
        this.parent = parent;
    }

    // Listen for the control's window creation and then hook into it.
    internal void OnHandleCreated(object sender, EventArgs e)
    {
        // Window is now created, assign handle to NativeWindow.
        AssignHandle(((Form1)sender).Handle);
    }
    internal void OnHandleDestroyed(object sender, EventArgs e)
    {
        // Window was destroyed, release hook.
        ReleaseHandle();
    }

    protected override void WndProc(ref Message m)
    {
        // Listen for operating system messages

        switch (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(((int)m.WParam != 0));

                break;
        }
        base.WndProc(ref m);
    }
}

' 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

Remarks

This method is called when a window message is sent to the handle of the window.

Notes to Inheritors

Override this method to implement specific message processing. Call base.WndProc for unhandled messages.

Applies to

See also