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前言

一切的起因就是Silverlight对F10键根本没有响应。在按F10键时，根本不会触发KeyDown事件。

Silverlight5之前的版本我不太清楚，不过Silverlight5新特性中有使用P/Invoke调用非托管代码。既然这样，做个键盘钩子不就解决了？我喜欢DllImport。

正文

先了解钩子相关的信息(SetWindowsHookEx、UnhookWindowsHookEx)，下面是原生代码。

   1: private delegate int HookProc(int nCode, Int32 wParam, IntPtr lParam);

   2:  

   3: [DllImport("user32.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]

   4: private static extern int SetWindowsHookEx(int idHook, HookProc lpfn, IntPtr hInstance, int threadId);

   5:  

   6: [DllImport("user32.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]

   7: private static extern bool UnhookWindowsHookEx(int idHook);

   8:  

   9: [DllImport("user32.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]

  10: private static extern int CallNextHookEx(int idHook, int nCode, Int32 wParam, IntPtr lParam);

  11:  

  12: [DllImport("kernel32.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]

  13: private static extern IntPtr GetModuleHandle(string lpModuleName);

其中委托HookProc用于设置钩子的回调函数。

处理回调的时候还会用到键盘钩子的封送结构。

   1: [StructLayout(LayoutKind.Sequential)]

   2: private class KeyboardHookStruct

   3: {

   4:     public int vkCode; //表示一个在1到254间的虚似键盘码 

   5:     public int scanCode; 

   6:     public int flags;

   7:     public int time;

   8:     public int dwExtraInfo;

   9: }

以下为主体代码。

   1: //常量

   2: private const int WH_KEYBOARD_LL = 13; //低级键盘钩子

   3: private const int WM_KEYDOWN = 0x100;

   4: private const int WM_SYSKEYDOWN = 0x104;

   5:  

   6: private static int iKeyboardHook; //钩子句柄

   7: HookProc HookProcDelegate;

   8:  

   9: //回调函数

  10: [AllowReversePInvokeCalls]

  11: private int HookProcHandler(int nCode, Int32 wParam, IntPtr lParam)

  12: {

  13:     //可以增加当前窗口是否是活动窗口的判断，不然低级键盘钩子还会截获所有的键盘消息

  14:     //可以使用App.Current.MainWindow.IsActive

  15:     KeyboardHookStruct khs = new KeyboardHookStruct();

  16:     Marshal.PtrToStructure(lParam, khs);

  17:     //KeyDown

  18:     if (wParam == WM_KEYDOWN || wParam == WM_SYSKEYDOWN)

  19:     {

  20:         if (khs.vkCode == 0x79) //F10

  21:         {

  22:             //Do something

  23:         }

  24:     }

  25:     return CallNextHookEx(iKeyboardHook, nCode, wParam, lParam);

  26: }

  27:  

  28: /// <summary>

  29: /// 注册键盘钩子

  30: /// </summary>

  31: public void Hook()

  32: {

  33:     IntPtr ip = GetModuleHandle(System.Reflection.Assembly.GetExecutingAssembly().GetModules()[0].Name);

  34:     HookProcDelegate = new HookProc(HookProcHandler);

  35:     iKeyboardHook = SetWindowsHookEx(13, HookProcDelegate, ip, 0);

  36:     if (iKeyboardHook == 0)

  37:     {

  38:         throw new Exception("注册键盘钩子失败");

  39:     }

  40: }

  41:  

  42: /// <summary>

  43: /// 卸载键盘钩子

  44: /// </summary>

  45: public void UnHook()

  46: {

  47:     if (!UnhookWindowsHookEx(iKeyboardHook))

  48:     {

  49:         throw new Exception("卸载键盘钩子失败");

  50:     }

  51:     iKeyboardHook = 0;

  52: }

回调函数的AllowReversePInvokeCalls属性允许非托管方法调用托管方法。

结语

现在截获F10就是小意思了。还可以根据这些封装一下，不过暂时不需要就先这样了。

Tips:

1. 注册钩子时SetWindowsHookEx函数的threadId参数设置为0，所以需要在回调函数里判断当前Silverlight窗体是否为活动窗体。

2. KeyboardHookStruct.vkCode对应的键值是System.Windows.Forms命名空间里Keys枚举的键值，所以判断是否是F10键时用的是0x79，而不是System.Windows.Input命名空间里Key枚举的65。