通过调用API函数实现的无边框窗体的拖拽，比判断坐标更快捷

#region 移动无边框窗体事件
private void form1_MouseDown(object sender, MouseEventArgs e)
{
ReleaseCapture();
SendMessage(this.Handle, WM_SYSCOMMAND, SC_MOVE + HTCAPTION, 0);//*********************调用移动无窗体控件函数
}
#endregion

#region 拖动无边框窗体
[DllImport("user32.dll")]//*********************拖动无窗体的控件
public static extern bool ReleaseCapture();
[DllImport("user32.dll")]
public static extern bool SendMessage(IntPtr hwnd, int wMsg, int wParam, int lParam);
public const int WM_SYSCOMMAND = 0x0112;
public const int SC_MOVE = 0xF010;
public const int HTCAPTION = 0x0002;
#endregion

这样就能轻松实现窗体拖拽！