C# WinForm 中在窗口标题栏上加按钮

实现主要是通过重写窗口过程（WndProc），处理一些非客户区消息（WM_NCxxxx);

 1 [DllImport( " User32.dll " )]
 2          private   static   extern  IntPtr GetWindowDC(IntPtr hwnd);
 3         [DllImport( " User32.dll " )]
 4          private   static   extern   int  ReleaseDC(IntPtr hwnd, IntPtr hdc);
 5         [DllImport( " Kernel32.dll " )]
 6          private   static   extern   int  GetLastError();
 7          // 标题栏按钮的矩形区域。 
 8         Rectangle m_rect  =   new  Rectangle( 100 ,  6 ,  120 ,  20 );
 9          protected   override   void  WndProc( ref  Message m)
10          {
11            base.WndProc(ref m);
12            switch (m.Msg)
13            {
14                case 0x86://WM_NCACTIVATE 
15                    goto case 0x85;
16                case 0x85://WM_NCPAINT 
17                    {
18                        IntPtr hDC = GetWindowDC(m.HWnd);
19                        //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 
20                        Graphics gs = Graphics.FromHdc(hDC);
21                        gs.FillRectangle(new LinearGradientBrush(m_rect, Color.Pink, Color.Purple, LinearGradientMode.BackwardDiagonal), m_rect);
22                        StringFormat strFmt = new StringFormat();
23                        strFmt.Alignment = StringAlignment.Center;
24                        strFmt.LineAlignment = StringAlignment.Center;
25                        gs.DrawString("√", this.Font, Brushes.BlanchedAlmond, m_rect, strFmt);
26                        gs.Dispose();
27                        //释放GDI资源
28                        ReleaseDC(m.HWnd, hDC);
29                        break;
30                    }
31                case 0xA1://WM_NCLBUTTONDOWN 
32                    {
33                        Point mousePoint = new Point((int)m.LParam);
34                        mousePoint.Offset(-this.Left, -this.Top);
35                        if (m_rect.Contains(mousePoint))
36                        {
37                            MessageBox.Show("hello");
38                        }
39                        break;
40                    }
41            }
42        }

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）.