C# Windows Forms WndProc Examples

Let us look at a simple C# Windows Forms WndProc example.

Example 1: WndProc

This example will comprise the following files:

  • WndProc.cs

Step 1: Create Project

  1. The first step is to create a C# Project.
  2. Go to FILE-->New-->Project to create a new project.

Step 2: Write Code

Write Code as follows:

*(a). WndProc.cs

Create a file named WndProc.cs

Here is the full code

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

namespace Examples {
  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;

    public static void Main() {
      Application.Run(new Form1());

    Form1() {
      this.ClientSize = new System.Drawing.Size(300, 300);
      this.Text = "Form1";
      this.Font = new System.Drawing.Font("Microsoft Sans Serif", 18.0f, System.Drawing.FontStyle.Bold, System.Drawing.GraphicsUnit.Point, (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.MenuHighlight, 20, 20, 260, 50);
        e.Graphics.DrawString("Application is active", this.Font, SystemBrushes.ControlText, 20, 20);
      } else {
        e.Graphics.FillRectangle(SystemBrushes.Control, 20, 20, 260, 50);
        e.Graphics.DrawString("Application is Inactive", this.Font, SystemBrushes.ControlText, 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.
      base.WndProc(ref m);


Simply copy the source code into your C# Project,Build and Run. Alternatively download the code using the links provided below, then open the .csproj project, build and run.


Download the code using the below links:

Number Link
1. Download Example
2. Follow code author

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