关于hook键盘

学习hook，看到这个例子，说是输入b，结果输出是a，调试成功，但是运行输入什么输出还是什么，怎么回事呀，好像钩不到。using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;namespace ABturn
{
    public partial class Form1 : Form
    {
       
        internal enum HookType
        {
            //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, 
        };
        IntPtr _nextHookPtr;    //记录hook编号 
        [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);
        internal delegate IntPtr HookProc(int code, IntPtr wparam, IntPtr lparam);
        IntPtr MyHookProc(int code, IntPtr wparam, IntPtr lparam)
        {
            if (code < 0)
                return CallNextHookEx(_nextHookPtr, code, wparam, lparam);
            if (wparam.ToInt32() == 98 || wparam.ToInt32() == 66)
            {
               
                this.textBox1.Text = "a";
                return (IntPtr)1;
            }
            else
            {
                return IntPtr.Zero;
            }
        }        public void SetHook()
        {
            if (_nextHookPtr != IntPtr.Zero)
                return;            HookProc myhookProc = new HookProc(MyHookProc);
            _nextHookPtr = SetWindowsHookEx((int)HookType.Keyboard , myhookProc, IntPtr.Zero, GetCurrentThreadId());
        }
        public void UnHook()
        {
            if (_nextHookPtr != IntPtr.Zero)
            {
                UnhookWindowsHookEx(_nextHookPtr);
                _nextHookPtr = IntPtr.Zero;
            }
        }
        public Form1()
        {
            InitializeComponent();
        }        private void Form1_Load(object sender, EventArgs e)
        {
            SetHook();
        }
        private void Form1_Closing(object sender, System.ComponentModel.CancelEventArgs e)
        {
            UnHook();
        }     }
}