无需重点即可捕获击键

Question

例如，使用winamp（至少在Windows上），您可以在后台以winamp播放全屏游戏，并使用媒体按钮*控制声音。Winamp不需要聚焦，可以使游戏继续全屏显示。

我更喜欢用Java编写此代码，但这可能行不通（在Java afaik中很难捕获没有重点的击键），因此任何C＃解决方案也都可以。

因此，基本问题是：如何在没有重点的情况下捕获击键？

*）我相信“后退/前进/停止/邮件/搜索/收藏夹/网站/主页”按钮称为媒体按钮，但欢迎使用更好的名称:)。

Answer 1

低级Windows挂钩是一种实现方法。这是一篇文章，这里是来自MSDN的更多信息。

这是该代码的局部视图：

    private IntPtr LowLevelKeyboardHook(int nCode, WindowsMessages wParam, [In] KBDLLHOOKSTRUCT lParam)
    {
        bool callNext = true;

        bool isKeyDown = (wParam == WindowsMessages.KEYDOWN || wParam == WindowsMessages.SYSKEYDOWN);
        bool isKeyUp = (wParam == WindowsMessages.KEYUP || wParam == WindowsMessages.SYSKEYUP);

        if ((nCode >= 0) && (isKeyDown || isKeyUp))
        {
            // the virtual key codes and the winforms Keys have the same enumeration
            // so we can freely cast back and forth between them
            Keys key = (Keys)lParam.vkCode;

            // Do your other processing here...
        }

        // if any handler returned false, trap the message
        return (callNext) ? User32.CallNextHookEx(_mainHook, nCode, wParam, lParam) : _nullNext;
    }


    /// <summary>
    /// Registers the user's LowLevelKeyboardProc with the system in order to
    /// intercept any keyboard events before processed in the regular fashion.
    /// This can be used to log all keyboard events or ignore them.
    /// </summary>
    /// <param name="hook">Callback function to call whenever a keyboard event occurs.</param>
    /// <returns>The IntPtr assigned by the Windows's sytem that defines the callback.</returns>
    private IntPtr RegisterLowLevelHook(LowLevelKeyboardProc hook)
    {
        IntPtr handle = IntPtr.Zero;

        using (Process currentProcess = Process.GetCurrentProcess())
        using (ProcessModule currentModule = currentProcess.MainModule)
        {
            IntPtr module = Kernel32.GetModuleHandle(currentModule.ModuleName);
            handle = User32.SetWindowsHookEx(HookType.KEYBOARD_LL, hook, module, 0);
        }

        return handle;
    }

    /// <summary>
    /// Unregisters a previously registered callback from the low-level chain.
    /// </summary>
    /// <param name="hook">IntPtr previously assigned to the low-level chain.
    /// Users should have stored the value given by 
    /// <see cref="Drs.Interop.Win32.LowLevelKeyboard.RegisterLowLevelHook"/>,
    /// and use that value as the parameter into this function.</param>
    /// <returns>True if the hook was removed, false otherwise.</returns>
    private bool UnregisterLowLevelHook(IntPtr hook)
    {
        return User32.UnhookWindowsHookEx(hook);
    }

只需实现所需的所有P / Invoke声明，它就可以工作。我在应用程序中使用了这种方法，并且效果很好。