CheckedListBox::WndProc Method (Message%)

 

Processes Windows messages.

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

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

Parameters

m
Type: System.Windows.Forms::Message%

The Windows Message to process.

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. Refer to the Platform SDK documentation reference located in the MSDN Library at http://msdn.microsoft.com/library to understand the available Message::Msg, Message::LParam, and Message::WParam values. Actual constant values can be found in the Windows.h header file included in the Platform SDK (Core SDK section) download, which is also available in the MSDN Library at http://msdn.microsoft.com/library.

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 );
}

SecurityPermission

for operating with unmanaged code. Associated enumeration: UnmanagedCode

.NET Framework
Available since 1.1
Return to top
Show: