C# 键盘钩子

键盘钩子是一种可以监控键盘操作的指令，我们去钓鱼只要鱼儿上钩不管它怎么逃，只要掌控好钩子上的绳子总是可以找到这条鱼，键盘钩子是利用电脑一行行执行代码特性，在目的窗口处理键代码前拦截把某个指令替换为另外一种指令，然后再把消息传送给目的窗口这样一个周期下来，窗口程序会认为用户输入的就是现在的数值或者没有输入，不过键盘钩子在某些不法分子手里则成为了 盗号、监控密码 等违法操作。原型：HHOOK SetWindowsHookEx(int idHook, HOOKPROC lpfn, HINSTANCE hMod, DWORD dwThreadId);

// Win32 keyboard hook.
public const int WH_KEYBOARD_LL = 13;
public const int NULL = 0;
 
public delegate int HookProc(int code, int wParam, KBDLLHOOKSTRUCT lParam);
 
[DllImport("user32.dll", SetLastError = true)]
public static extern int SetWindowsHookEx(int hookType, HookProc lpfn, int hMod, int dwThreadId);
 
[DllImport("User32.dll", SetLastError = true)]
public extern static int CallNextHookEx(int handle, int code, int wParam, KBDLLHOOKSTRUCT lParam);
 
[StructLayout(LayoutKind.Sequential)]
public class KBDLLHOOKSTRUCT
{
    public uint vkCode;
    public uint scanCode;
    public KBDLLHOOKSTRUCT flags;
    public uint time;
    public UIntPtr dwExtraInfo;
}
 
[Flags]
public enum KBDLLHOOKSTRUCT : uint
{
    LLKHF_EXTENDED = 0x01,
    LLKHF_INJECTED = 0x10,
    LLKHF_ALTDOWN = 0x20,
    LLKHF_UP = 0x80,
}
 
public volatile int hHook;
 
protected override void OnLoad(EventArgs e)
{
    base.OnLoad(e);
    // 安装全局键盘钩子
    if ((this.hHook = SetWindowsHookEx(WH_KEYBOARD_LL, this.KeyBoardProc, NULL, NULL)) == NULL)
        Console.WriteLine("Unable to establish a keyboard hook.");
}
 
protected int KeyBoardProc(int code, int wParam, KBDLLHOOKSTRUCT lParam)
{
    if (lParam.vkCode == (int)Keys.A)
        return 1; // 返回1表示拦截消息，返回0表示放行
    return CallNextHookEx(hHook, code, wParam, lParam);
}

监控系统内所有进程键盘消息：
SetWindowsHookEx(WH_KEYBOARD_LL, KeyBoardProc, NULL, NULL)

        // Win32 keyboard hook.
        public const int WH_KEYBOARD = 2;
        public const int NULL = 0;
 
        public delegate int HookProc(int code, int wParam, int lParam);
 
        [DllImport("kernel32.dll", SetLastError = true)]
        public static extern int GetCurrentThreadId();
 
        [DllImport("user32.dll", SetLastError = true)]
        public static extern int SetWindowsHookEx(int hookType, HookProc lpfn, int hMod, int dwThreadId);
 
        [DllImport("User32.dll", SetLastError = true)]
        public extern static int CallNextHookEx(int handle, int code, int wParam, int lParam);
 
        public volatile int hHook;
 
        protected override void OnLoad(EventArgs e)
        {
            base.OnLoad(e);
            // 安装键盘钩子
if ((this.hHook = SetWindowsHookEx(WH_KEYBOARD, KeyBoardProc, NULL, 
GetCurrentThreadId())) == NULL) Console.WriteLine("Unable to establish a
 keyboard hook."); }
protected int KeyBoardQueue(int code, int wParam, int lParam)
{
    if (wParam == (int)Keys.A)
       
 return 1; // 
返回1表示拦截消息，返回0表示放行
    return CallNextHookEx(hHook, code, wParam, lParam);
}
监控本进程的所有键盘消息：
     SetWindowsHookEx(WH_KEYBOARD, KeyBoardProc, NULL, GetCurrentThreadId());
protected int KeyBoardProc(int code, int wParam, int lParam)
   {
       if (wParam == (int)Keys.A)
           return 1;
       return CallNextHookEx(hHook, code, wParam, lParam);
   }