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;
}
}
}