C# WinForm 中在窗口标题栏上加按钮

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
{
  /// <summary>
  /// Form1 的摘要说明。
  /// </summary>
  public class Form1 : System.Windows.Forms.Form
  {
  /// <summary>
  /// 必需的设计器变量。
  /// </summary>
  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
  //
  }

  /// <summary>
  /// 清理所有正在使用的资源。
  /// </summary>
  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

  /// <summary>
  /// 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。
  /// </summary>
  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

  /// <summary>
  /// 应用程序的主入口点。
  /// </summary>
  [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, 4, 16, 16);

  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 = 4;
  m_rect.Width = m_rect.Height = 16;
  }
  }
}