[Silverlight]鍵盤鈎子KeyboardHook

前言

一切的起因就是Silverlight對F10鍵根本沒有響應。在按F10鍵時，根本不會觸發KeyDown事件。

Silverlight5之前的版本我不太清楚，不過Silverlight5新特性中有使用P/Invoke調用非托管代碼。既然這樣，做個鍵盤鈎子不就解決了？我喜歡DllImport。

正文

先了解鈎子相關的信息(SetWindowsHookEx、UnhookWindowsHookEx)，下面是原生代碼。

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

[DllImport("user32.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]
private static extern int SetWindowsHookEx(int idHook, HookProc lpfn, IntPtr hInstance, int threadId);

[DllImport("user32.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]
private static extern bool UnhookWindowsHookEx(int idHook);

[DllImport("user32.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]
private static extern int CallNextHookEx(int idHook, int nCode, Int32 wParam, IntPtr lParam);

[DllImport("kernel32.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]
private static extern IntPtr GetModuleHandle(string lpModuleName);

其中委托HookProc用於設置鈎子的回調函數。

處理回調的時候還會用到鍵盤鈎子的封送結構。

[StructLayout(LayoutKind.Sequential)]
private class KeyboardHookStruct
{
    public int vkCode; //表示一個在1到254間的虛似鍵盤碼
    public int scanCode;
    public int flags;
    public int time;
    public int dwExtraInfo;
}

以下為主體代碼。

//常量
private const int WH_KEYBOARD_LL = 13; //低級鍵盤鈎子
private const int WM_KEYDOWN = 0x100;
private const int WM_SYSKEYDOWN = 0x104;

private static int iKeyboardHook; //鈎子句柄
HookProc HookProcDelegate;

//回調函數
[AllowReversePInvokeCalls]
private int HookProcHandler(int nCode, Int32 wParam, IntPtr lParam)
{
    //可以增加當前窗口是否是活動窗口的判斷，不然低級鍵盤鈎子還會截獲所有的鍵盤消息
    //可以使用App.Current.MainWindow.IsActive
    KeyboardHookStruct khs = new KeyboardHookStruct();
    Marshal.PtrToStructure(lParam, khs);
    //KeyDown
    if (wParam == WM_KEYDOWN || wParam == WM_SYSKEYDOWN)
    {
        if (khs.vkCode == 0x79) //F10
        {
            //Do something
        }
    }
    return CallNextHookEx(iKeyboardHook, nCode, wParam, lParam);
}

/// <summary>
/// 注冊鍵盤鈎子
/// </summary>
public void Hook()
{
    IntPtr ip = GetModuleHandle(System.Reflection.Assembly.GetExecutingAssembly().GetModules()[0].Name);
    HookProcDelegate = new HookProc(HookProcHandler);
    iKeyboardHook = SetWindowsHookEx(13, HookProcDelegate, ip, 0);
    if (iKeyboardHook == 0)
    {
        throw new Exception("注冊鍵盤鈎子失敗");
    }
}

/// <summary>
/// 卸載鍵盤鈎子
/// </summary>
public void UnHook()
{
    if (!UnhookWindowsHookEx(iKeyboardHook))
    {
        throw new Exception("卸載鍵盤鈎子失敗");
    }
    iKeyboardHook = 0;
}

回調函數的AllowReversePInvokeCalls屬性允許非托管方法調用托管方法。

結語

現在截獲F10就是小意思了。還可以根據這些封裝一下，不過暫時不需要就先這樣了。

Tips:

1. 注冊鈎子時SetWindowsHookEx函數的threadId參數設置為0，所以需要在回調函數里判斷當前Silverlight窗體是否為活動窗體。

2. KeyboardHookStruct.vkCode對應的鍵值是System.Windows.Forms命名空間里Keys枚舉的鍵值，所以判斷是否是F10鍵時用的是0x79，而不是System.Windows.Input命名空間里Key枚舉的65。