WndProc Method

MenuStrip.WndProc Method (Message)


Processes Windows messages.

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

[SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags = SecurityPermissionFlag.UnmanagedCode)]
protected override void WndProc(
	ref 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 documentation in the Windows Platform SDK reference located in the MSDN library at http://msdn.microsoft.com/library.

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. 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 on MSDN.

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;

        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.DrawString("Application is active", this.Font, SystemBrushes.ActiveCaptionText, 20,20);
                e.Graphics.DrawString("Application is Inactive", this.Font, SystemBrushes.ActiveCaptionText, 20,20);

	[System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name="FullTrust")]
        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.

            base.WndProc(ref m);

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

.NET Framework
Available since 2.0
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