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POUsing global keyboard hook (WH_KEYBOARD_LL) in WPF / C#
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copied!<p>I stitched together from code I found in internet myself <code>WH_KEYBOARD_LL</code> helper class:</p> <p>Put the following code to some of your utils libs, let it be <strong>YourUtils.cs</strong>:</p> <pre><code>using System; using System.Diagnostics; using System.Runtime.InteropServices; using System.Runtime.CompilerServices; using System.Windows.Input; namespace MYCOMPANYHERE.WPF.KeyboardHelper { public class KeyboardListener : IDisposable { private static IntPtr hookId = IntPtr.Zero; [MethodImpl(MethodImplOptions.NoInlining)] private IntPtr HookCallback( int nCode, IntPtr wParam, IntPtr lParam) { try { return HookCallbackInner(nCode, wParam, lParam); } catch { Console.WriteLine("There was some error somewhere..."); } return InterceptKeys.CallNextHookEx(hookId, nCode, wParam, lParam); } private IntPtr HookCallbackInner(int nCode, IntPtr wParam, IntPtr lParam) { if (nCode >= 0) { if (wParam == (IntPtr)InterceptKeys.WM_KEYDOWN) { int vkCode = Marshal.ReadInt32(lParam); if (KeyDown != null) KeyDown(this, new RawKeyEventArgs(vkCode, false)); } else if (wParam == (IntPtr)InterceptKeys.WM_KEYUP) { int vkCode = Marshal.ReadInt32(lParam); if (KeyUp != null) KeyUp(this, new RawKeyEventArgs(vkCode, false)); } } return InterceptKeys.CallNextHookEx(hookId, nCode, wParam, lParam); } public event RawKeyEventHandler KeyDown; public event RawKeyEventHandler KeyUp; public KeyboardListener() { hookId = InterceptKeys.SetHook((InterceptKeys.LowLevelKeyboardProc)HookCallback); } ~KeyboardListener() { Dispose(); } #region IDisposable Members public void Dispose() { InterceptKeys.UnhookWindowsHookEx(hookId); } #endregion } internal static class InterceptKeys { public delegate IntPtr LowLevelKeyboardProc( int nCode, IntPtr wParam, IntPtr lParam); public static int WH_KEYBOARD_LL = 13; public static int WM_KEYDOWN = 0x0100; public static int WM_KEYUP = 0x0101; public static IntPtr SetHook(LowLevelKeyboardProc proc) { using (Process curProcess = Process.GetCurrentProcess()) using (ProcessModule curModule = curProcess.MainModule) { return SetWindowsHookEx(WH_KEYBOARD_LL, proc, GetModuleHandle(curModule.ModuleName), 0); } } [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)] public static extern IntPtr SetWindowsHookEx(int idHook, LowLevelKeyboardProc lpfn, IntPtr hMod, uint dwThreadId); [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)] [return: MarshalAs(UnmanagedType.Bool)] public static extern bool UnhookWindowsHookEx(IntPtr hhk); [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)] public static extern IntPtr CallNextHookEx(IntPtr hhk, int nCode, IntPtr wParam, IntPtr lParam); [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)] public static extern IntPtr GetModuleHandle(string lpModuleName); } public class RawKeyEventArgs : EventArgs { public int VKCode; public Key Key; public bool IsSysKey; public RawKeyEventArgs(int VKCode, bool isSysKey) { this.VKCode = VKCode; this.IsSysKey = isSysKey; this.Key = System.Windows.Input.KeyInterop.KeyFromVirtualKey(VKCode); } } public delegate void RawKeyEventHandler(object sender, RawKeyEventArgs args); } </code></pre> <p>Which I use like this:</p> <p><strong>App.xaml</strong>:</p> <pre><code><Application ... Startup="Application_Startup" Exit="Application_Exit"> ... </code></pre> <p><strong>App.xaml.cs</strong>:</p> <pre><code>public partial class App : Application { KeyboardListener KListener = new KeyboardListener(); private void Application_Startup(object sender, StartupEventArgs e) { KListener.KeyDown += new RawKeyEventHandler(KListener_KeyDown); } void KListener_KeyDown(object sender, RawKeyEventArgs args) { Console.WriteLine(args.Key.ToString()); // I tried writing the data in file here also, to make sure the problem is not in Console.WriteLine } private void Application_Exit(object sender, ExitEventArgs e) { KListener.Dispose(); } } </code></pre> <p>The problem is that it <strong>stops working after hitting keys a while</strong>. No error is raised what so ever, I just don't get anything to output after a while. I can't find a solid pattern when it stops working.</p> <p>Reproducing this problem is quiet simple, hit some keys like a mad man, usually outside the window.</p> <p>I suspect there is some evil <em>threading problem</em> behind, anyone got idea how to keep this working?</p> <hr> <p>What I tried already:</p> <ol> <li>Replacing <code>return HookCallbackInner(nCode, wParam, lParam);</code> with something simple.</li> <li>Replacing it with asynchronous call, trying to put Sleep 5000ms (etc).</li> </ol> <p>Asynchronous call didn't make it work any better, it seems stop always when user keeps single letter down for a while.</p>

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