WinForm 求教如何捕获窗口外的鼠标事件 SetCapture

WinForm 求教怎么捕获窗口外的鼠标事件 SetCapture
我有一个模态对话框想在鼠标点击窗口外的地方时执行一段代码
var form=new Form1();
form.showDialog();

有人说用 SetCapture();

我在form中加了SetCapture(this) 后该怎么做
WndProc(ref Message m) 里还是得不到鼠标的消息
 

------最佳解决方案--------------------------------------------------------

        [DllImport("user32.dll")]
        public static extern bool ReleaseCapture();

        [DllImport("user32.dll")]
        public static extern IntPtr SetCapture(IntPtr h);

        private void Form2_Load(object sender, EventArgs e)
        {
            SetCapture(this.Handle);
        }

        private void Form2_FormClosing(object sender, FormClosingEventArgs e)
        {
            ReleaseCapture();
        }

        private void Form2_MouseUp(object sender, MouseEventArgs e)
        {
            Close();
        }

------其他解决方案--------------------------------------------------------
这次好像粘错代码了


------其他解决方案--------------------------------------------------------

using System;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        [DllImport("user32.dll")]
        public static extern bool ReleaseCapture();

        [DllImport("user32.dll")]
        public static extern IntPtr SetCapture(IntPtr h);

        private readonly Int32 WM_LBUTTONUP = 0x202;

        private void Form1_Load(object sender, EventArgs e)
        {
            SetCapture(this.Handle);
        }

        private void Form1_FormClosing(object sender, FormClosingEventArgs e)
        {
            ReleaseCapture();
        }

        protected override void WndProc(ref Message m)