c# 的 Form 是如何封裝 WndProc 方法的

1. 類繼承關係

System.Object
 System.MarshalByRefObject
  System.ComponentModel.Component
   System.Windows.Forms.Control
    System.Windows.Forms.ScrollableControl
      System.Windows.Forms.ContainerControl
        System.Windows.Forms.Form
        System.ComponentModel.Design.CollectionEditor.CollectionForm
        System.Messaging.Design.QueuePathDialog
        System.ServiceProcess.Design.ServiceInstallerDialog
        System.Web.UI.Design.WebControls.CalendarAutoFormatDialog
        System.Web.UI.Design.WebControls.RegexEditorDialog
        System.Windows.Forms.Design.ComponentEditorForm
        System.Windows.Forms.PrintPreviewDialog
        System.Windows.Forms.ThreadExceptionDialog
        System.Workflow.Activities.Rules.Design.RuleConditionDialog
        System.Workflow.Activities.Rules.Design.RuleSetDialog
        System.Workflow.ComponentModel.Design.ThemeConfigurationDialog
        System.Workflow.ComponentModel.Design.TypeBrowserDialog
        System.Workflow.ComponentModel.Design.WorkflowPageSetupDialog

WndProc 方法所在的類

System.Windows.Forms.Control

WndProc Processes Windows messages.

結論

Form 類都是由 WndProc 方法的，我們可以重載它來實現自己的功能。實例如下：

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);
            }
        }

	[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.
                    this.Invalidate();

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