Control::WndProc Method (Message%)


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Processes Windows messages.

Namespace:   System.Windows.Forms
Assembly:  System.Windows.Forms (in System.Windows.Forms.dll)

	Flags = SecurityPermissionFlag::UnmanagedCode)]
[SecurityPermissionAttribute(SecurityAction::LinkDemand, Flags = SecurityPermissionFlag::UnmanagedCode)]
virtual void WndProc(
	Message% m


Type: System.Windows.Forms::Message%

The Windows Message to process.

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 method to process any messages that they do not handle.

The following code example demonstrates overriding the WndProc method to handle operating system messages identified in the Message structure. TheWM_ACTIVATEAPPoperating 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

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

         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)) );

      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 );
            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.
         Form::WndProc( m );



int main()
   Application::Run( gcnew csTempWindowsApplication1::Form1 );


for inheriting classes to call unmanaged code. Associated enumeration: SecurityPermissionFlag::UnmanagedCode.


for the immediate caller to call unmanaged code. Associated enumeration: SecurityPermissionFlag::UnmanagedCode.

.NET Framework
Available since 1.1
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