C# WinForm 中在窗口标题栏上加按钮

在窗口标题栏上加按钮本来不是什么新鲜事了，我在VC++下早也实现过了（相信很多人也都实现过了）。今天一个朋友问我C# WinForm下可否实现，我就顺便拿C#写了一个。
   原理是一样的，都是重写窗口过程（WndProc），处理一些非客户区消息（WM_NCxxxx），可以说本来没有什么新意，可是从写这个程序的过程中，我也学到了两个技巧：
    1）、C#中重写窗口过程不用再调用SetWindowLong API了，直接overide一个WndProc就可以了。
    2）、Windows API中的HDC可以通过Graphics.FromHdc()转换为(创建出)System.Drawing.Graphics，然后就可以用.NET Framework （GID+??）提供的绘图功能方便地进行画图了。终于可以抛开讨厌的GDI API了（说实在话，在C#中调用Windows API真的太麻烦了:)）.
代码如下：
using System;using System.Drawing;using System.Drawing.Drawing2D;using System.Collections;using System.ComponentModel;using System.Windows.Forms;using System.Data;using System.Runtime.InteropServices;using System.Diagnostics; namespace WindowsApplication2{    ///

    /// Form1 的摘要说明。    ///

    public class Form1 : System.Windows.Forms.Form    {        ///

        /// 必需的设计器变量。        ///

        private System.ComponentModel.Container components = null;         public Form1()        {            //            // Windows 窗体设计器支持所必需的            //            InitializeComponent();            //            // TODO: 在 InitializeComponent 调用后添加任何构造函数代码            //        }        ///

        /// 清理所有正在使用的资源。        ///

        protected override void Dispose( bool disposing )        {            if( disposing )            {                if (components != null)                 {                    components.Dispose();                }            }            base.Dispose( disposing );        }        #region Windows 窗体设计器生成的代码        ///

        /// 设计器支持所需的方法 - 不要使用代码编辑器修改        /// 此方法的内容。        ///

        private void InitializeComponent()        {            //             // Form1            //             this.AutoScaleBaseSize = new System.Drawing.Size(6, 14);            this.ClientSize = new System.Drawing.Size(292, 266);            this.Name = "Form1";            this.Text = "Form1";            this.SizeChanged += new System.EventHandler(this.Form1_SizeChanged);        }        #endregion        ///

        /// 应用程序的主入口点。        ///

        [STAThread]        static void Main()         {            Application.Run(new Form1());        }        [DllImport ("User32.dll")]        private static extern IntPtr GetWindowDC(IntPtr hwnd);        [DllImport ("User32.dll")]        private static extern int ReleaseDC(IntPtr hwnd, IntPtr hdc);        [DllImport ("Kernel32.dll")]        private static extern int GetLastError();            //标题栏按钮的矩形区域。        Rectangle m_rect = new Rectangle(205, 6, 20, 20);        protected override void WndProc(ref Message m)        {            base.WndProc(ref m);            switch(m.Msg)            {                case 0x86://WM_NCACTIVATE                    goto case 0x85;                case 0x85://WM_NCPAINT                {                    IntPtr hDC = GetWindowDC(m.HWnd);                    //把DC转换为.NET的Graphics就可以很方便地使用Framework提供的绘图功能了                    Graphics gs = Graphics.FromHdc(hDC);                    gs.FillRectangle(new LinearGradientBrush(m_rect, Color.Pink, Color.Purple, LinearGradientMode.BackwardDiagonal), m_rect);                    StringFormat strFmt = new StringFormat();                    strFmt.Alignment = StringAlignment.Center;                    strFmt.LineAlignment = StringAlignment.Center;                    gs.DrawString("√", this.Font, Brushes.BlanchedAlmond, m_rect, strFmt);                    gs.Dispose();                    //释放GDI资源                    ReleaseDC(m.HWnd, hDC);                    break;                }                case 0xA1://WM_NCLBUTTONDOWN                {                    Point mousePoint = new Point((int)m.LParam);                    mousePoint.Offset(-this.Left, -this.Top);                    if(m_rect.Contains(mousePoint))                    {                        MessageBox.Show("hello");                    }                    break;                }            }        }        //在窗口大小改变时及时更新按钮的区域。        private void Form1_SizeChanged(object sender, System.EventArgs e)        {            m_rect.X = this.Bounds.Width - 95;            m_rect.Y = 6;            m_rect.Width = m_rect.Height = 20;        }    }}