class ThreadHandler
{#region P/Invoking and constants definitionconst uint WM_GETTEXT = 0x000D;[DllImport("user32.dll")]static extern IntPtr SetFocus(IntPtr hWnd);[DllImport("user32.dll")]private static extern int GetWindowThreadProcessId(IntPtr hWnd, uint lpdwProcessId = 0);delegate bool EnumThreadDelegate(IntPtr hWnd, IntPtr lParam);[DllImport("user32.dll")]static extern bool EnumThreadWindows(int dwThreadId, EnumThreadDelegate lpfn,IntPtr lParam);[DllImport("user32.dll")]static extern bool AttachThreadInput(int idAttach, int idAttachTo, bool fAttach);[DllImport("kernel32.dll")]static extern int GetCurrentThreadId();[DllImport("user32.dll", CharSet = CharSet.Auto)]static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, int wParam, StringBuilder lParam);#endregionpublic readonly string ProcessName, WindowName;protected readonly int TargetThreadID, CurrentThreadID;protected readonly IntPtr TargetWindowHandle;public ThreadHandler(string processName, string windowName){CurrentThreadID = GetCurrentThreadId();ProcessName = processName;WindowName = windowName;object[] objs = GetWindowThread(processName, windowName);if (objs == null){throw new ArgumentException("Could not find the specified process/window.");}TargetThreadID = (int)objs[0];TargetWindowHandle = (IntPtr)objs[1];}public ThreadHandler(string processName){CurrentThreadID = GetCurrentThreadId();ProcessName = processName;var processes = Process.GetProcessesByName(ProcessName);if (processes.Length == 0){throw new ArgumentException("Could not find the specified process.");}var appProc = processes[0];WindowName = appProc.MainWindowTitle;TargetThreadID = GetWindowThreadProcessId(appProc.MainWindowHandle);TargetWindowHandle = appProc.MainWindowHandle;}public bool AttachThreadInput(){return AttachThreadInput(CurrentThreadID, TargetThreadID, true);}public bool DetachThreadInput(){return AttachThreadInput(CurrentThreadID, TargetThreadID, false);}public void SetFocus(){SetFocus(TargetWindowHandle);}static object[] GetWindowThread(string processName, string windowName){var processes = Process.GetProcessesByName(processName);if (processes.Length > 0){//Fill a list of handlesvar handles = new List<IntPtr>();foreach (ProcessThread thread in processes[0].Threads)EnumThreadWindows(thread.Id,(hWnd, lParam) => { handles.Add(hWnd); return true; }, IntPtr.Zero);//Create a stringbuilder to function as storage unitStringBuilder nameBuffer = new StringBuilder(64);foreach (var hWnd in handles){//And finally compare the caption of the window with the requested name
                nameBuffer.Clear();SendMessage(hWnd, WM_GETTEXT, nameBuffer.Capacity, nameBuffer);if (nameBuffer.ToString() == windowName){return new object[2] { GetWindowThreadProcessId(hWnd), hWnd };}}}return null;}
}

static void Main(string[] args){Console.WriteLine("Please input the name of the process to hook: ");string pName = Console.ReadLine();Console.WriteLine("Input the name of a specific window, or leave blank: ");string pWnd = Console.ReadLine();ThreadHandler threadHandler;try{if(!String.IsNullOrWhiteSpace(pWnd))threadHandler = new ThreadHandler(pName, pWnd);elsethreadHandler = new ThreadHandler(pName);}catch{Console.WriteLine("Error: " + pName +" does not seem to be running.");Console.ReadKey();return;}if (!threadHandler.AttachThreadInput()){Console.WriteLine("Error: The application tried to attach its Input Processing Mechanism to " + threadHandler.ProcessName + ", but failed.");Console.ReadKey();return;}Console.WriteLine("Input Processing Mechanism correctly attached to " + threadHandler.ProcessName + ".");threadHandler.SetFocus();InputSimulator.SimulateTextEntry("test"); //InputSimulator is a seemingly famous SendInput wrapper. Replacing this line with the code for a keystroke also doesn't work.
        Console.ReadLine();Console.WriteLine("Detaching Input Processing Mechanism.");threadHandler.DetachThreadInput();}