c# 全局钩子问题

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Reflection;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace wa_hooktest
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
internal enum HookType //枚举，钩子的类型
{

//MsgFilter = -1,

//JournalRecord = 0,

//JournalPlayback = 1,

Keyboard = 2,

//GetMessage = 3,

//CallWndProc = 4,

//CBT = 5,

//SysMsgFilter = 6,

//Mouse = 7,

//Hardware = 8,

//Debug = 9,

//Shell = 10,

//ForegroundIdle = 11,

//CallWndProcRet = 12,

KeyboardLL = 13,

//MouseLL = 14,

};

[DllImport("kernel32.dll")]
static extern int GetCurrentThreadId(); //取得当前线程编号的API

[DllImport("User32.dll")]
internal extern static void UnhookWindowsHookEx(IntPtr handle); //取消Hook的API


[DllImport("User32.dll")]
internal extern static IntPtr SetWindowsHookEx(int idHook, [MarshalAs(UnmanagedType.FunctionPtr)] HookProc lpfn, IntPtr hinstance, int threadID); //设置Hook的API


[DllImport("User32.dll")]
internal extern static IntPtr CallNextHookEx(IntPtr handle, int code, IntPtr wparam, IntPtr lparam); //取得下一个Hook的API
IntPtr _nextHookPtr; //记录Hook编号

public delegate IntPtr HookProc(int code, IntPtr wparam, IntPtr lparam);
public IntPtr MyHookProc(int code, IntPtr wparam, IntPtr lparam)
{
if (code < 0)
{
return CallNextHookEx(_nextHookPtr, code, wparam, lparam);
} //返回，让后面的程序处理该消息

if (wparam.ToInt32() == 98 || wparam.ToInt32() == 66)
{//如果用户输入的是 b

this.textBox1.Text = "a";
return (IntPtr)1; //直接返回了，该消息就处理结束了
}
else
{
return IntPtr.Zero; //返回，让后面的程序处理该消息
}



//if (wparam.ToInt32() == 91)
//{
// return (IntPtr)1;
//}
//else {
// return IntPtr.Zero;
//}
}

public void SetHook()
{

if (_nextHookPtr != IntPtr.Zero) //已经勾过了

return;
//线程钩子
HookProc myhookProc = new HookProc(MyHookProc); //声明一个自己的Hook实现函数的委托对象

//_nextHookPtr = SetWindowsHookEx((int)HookType.Keyboard, myhookProc, IntPtr.Zero, GetCurrentThreadId()); //加到Hook链中

//全局钩子
_nextHookPtr = SetWindowsHookEx((int)HookType.KeyboardLL, myhookProc, Marshal.GetHINSTANCE(Assembly.GetExecutingAssembly().GetModules()[0]), 0 ); //加到Hook链中

MessageBox.Show(_nextHookPtr.ToString());
}



public void UnHook()
{

if (_nextHookPtr != IntPtr.Zero)
{
UnhookWindowsHookEx(_nextHookPtr); //从Hook链中取消
_nextHookPtr = IntPtr.Zero;
}

}

private void Form1_Load(object sender, EventArgs e)
{
SetHook();
}

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