Control.WndProc(Message) Method

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

Examples

The following code example demonstrates overriding the WndProc method to handle operating system messages identified in the Message structure. The WM_ACTIVATEAPP operating system message is handled in this example to know when another application is becoming active. See the following topics to understand the available Message.Msg, Message.LParam, and Message.WParam values. Actual constant values can be found in the Windows.h header file.

using namespace System;
using namespace System::Drawing;
using namespace System::Windows::Forms;
using namespace System::Security::Permissions;

namespace csTempWindowsApplication1
{
 public ref class Form1: public System::Windows::Forms::Form
 {
 private:

 // Constant value was found in the "windows.h" header file.
 static const Int32 WM_ACTIVATEAPP = 0x001C;
 Boolean appActive;

 public:
 Form1()
 {
 appActive = true;
 this->Size = System::Drawing::Size( 300, 300 );
 this->Text = "Form1";
 this->Font = gcnew System::Drawing::Font( "Microsoft Sans Serif",18.0F,System::Drawing::FontStyle::Bold,System::Drawing::GraphicsUnit::Point,((System::Byte)(0)) );
 }


 protected:
 virtual void OnPaint( PaintEventArgs^ e ) override
 {
 
 // Paint a string in different styles depending on whether the
 // application is active.
 if ( appActive )
 {
 e->Graphics->FillRectangle( SystemBrushes::ActiveCaption, 20, 20, 260, 50 );
 e->Graphics->DrawString( "Application is active", this->Font, SystemBrushes::ActiveCaptionText, 20, 20 );
 }
 else
 {
 e->Graphics->FillRectangle( SystemBrushes::InactiveCaption, 20, 20, 260, 50 );
 e->Graphics->DrawString( "Application is Inactive", this->Font, SystemBrushes::ActiveCaptionText, 20, 20 );
 }
 }


 [SecurityPermission(SecurityAction::Demand, Flags=SecurityPermissionFlag::UnmanagedCode)]
 virtual void WndProc( Message% m ) override
 {
 
 // Listen for operating system messages.
 switch ( m.Msg )
 {
 case WM_ACTIVATEAPP:
 
 // The WParam value identifies what is occurring.
 appActive = (int)m.WParam != 0;
 
 // Invalidate to get new text painted.
 this->Invalidate();
 break;
 }
 Form::WndProc( m );
 }

 };

}


[STAThread]
int main()
{
 Application::Run( gcnew csTempWindowsApplication1::Form1 );
}

using System;
using System.Drawing;
using System.Windows.Forms;

namespace csTempWindowsApplication1
{
 public class Form1 : System.Windows.Forms.Form
 {
 // Constant value was found in the "windows.h" header file.
 private const int WM_ACTIVATEAPP = 0x001C;
 private bool appActive = true;

 [STAThread]
 static void Main() 
 {
 Application.Run(new Form1());
 }
 
 public Form1()
 {
 this.Size = new System.Drawing.Size(300,300);
 this.Text = "Form1";
 this.Font = new System.Drawing.Font("Microsoft Sans Serif", 18F, System.Drawing.FontStyle.Bold, System.Drawing.GraphicsUnit.Point, ((System.Byte)(0)));
 }

 protected override void OnPaint(PaintEventArgs e) 
 {
 // Paint a string in different styles depending on whether the
 // application is active.
 if (appActive) 
 {
 e.Graphics.FillRectangle(SystemBrushes.ActiveCaption,20,20,260,50);
 e.Graphics.DrawString("Application is active", this.Font, SystemBrushes.ActiveCaptionText, 20,20);
 }
 else 
 {
 e.Graphics.FillRectangle(SystemBrushes.InactiveCaption,20,20,260,50);
 e.Graphics.DrawString("Application is Inactive", this.Font, SystemBrushes.ActiveCaptionText, 20,20);
 }
 }

 protected override void WndProc(ref Message m) 
 {
 // Listen for operating system messages.
 switch (m.Msg)
 {
 // The WM_ACTIVATEAPP message occurs when the application
 // becomes the active application or becomes inactive.
 case WM_ACTIVATEAPP:

 // The WParam value identifies what is occurring.
 appActive = (((int)m.WParam != 0));

 // Invalidate to get new text painted.
 this.Invalidate();

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

Imports System.Drawing
Imports System.Windows.Forms

Namespace csTempWindowsApplication1

 Public Class Form1
 Inherits System.Windows.Forms.Form

 ' Constant value was found in the "windows.h" header file.
 Private Const WM_ACTIVATEAPP As Integer = &H1C
 Private appActive As Boolean = True

 <STAThread()> _
 Shared Sub Main()
 Application.Run(New Form1())
 End Sub

 Public Sub New()
 MyBase.New()

 Me.Size = New System.Drawing.Size(300, 300)
 Me.Text = "Form1"
 Me.Font = New System.Drawing.Font("Microsoft Sans Serif", 18.0!, System.Drawing.FontStyle.Bold, System.Drawing.GraphicsUnit.Point, CType(0, Byte))
 End Sub

 Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs)

 ' Paint a string in different styles depending on whether the
 ' application is active.
 If (appActive) Then
 e.Graphics.FillRectangle(SystemBrushes.ActiveCaption, 20, 20, 260, 50)
 e.Graphics.DrawString("Application is active", Me.Font, SystemBrushes.ActiveCaptionText, 20, 20)
 Else
 e.Graphics.FillRectangle(SystemBrushes.InactiveCaption, 20, 20, 260, 50)
 e.Graphics.DrawString("Application is Inactive", Me.Font, SystemBrushes.ActiveCaptionText, 20, 20)
 End If
 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)
 ' The WM_ACTIVATEAPP message occurs when the application
 ' becomes the active application or becomes inactive.
 Case WM_ACTIVATEAPP

 ' The WParam value identifies what is occurring.
 appActive = (m.WParam.ToInt32() <> 0)

 ' Invalidate to get new text painted.
 Me.Invalidate()

 End Select
 MyBase.WndProc(m)
 End Sub
 End Class
End Namespace

Remarks

All messages are sent to the WndProc method after getting filtered through the PreProcessMessage method.

The WndProc method corresponds exactly to the Windows WindowProc function. For more information about processing Windows messages, see the WindowProc function.

Notes to Inheritors

Inheriting controls should call the base class's WndProc(Message) method to process any messages that they do not handle.

See also

• PreProcessMessage(Message)
• DefWndProc(Message)