Question

I’m using a Keyboard hook in my XNA project (anyone who uses XNA knows how useless the built in keyboard class is for “text box” style typed input.

It works just fine for use in XNA projects, until forms are introduced. If I try to implement any form in the project, be it a custom form, or even just an OpenFileDialog, any key press inside a text box of the form is doubled, making typing just about impossible.

Does anyone know how I can stop the message from reaching the forms twice? perhaps by discarding the message when I get it? Perhaps there is a better solution? or perhaps its just something that cant be done.

Any help is appreciated.

EDIT:

Below is the keyboard hooking code I’m using, It may be familiar to anyone who’s gone looking for XNA keyboard hooking as it seems to crop up wherever I looked for it.

using System;
using System.Runtime.InteropServices;
using System.Windows.Forms; // This class exposes WinForms-style key events.

namespace FatLib.Controls
{
    class KeyboardHookInput : IDisposable
    {
        private string _buffer = "";
        private bool _backSpace = false;
        private bool _enterKey = false; // I added this to the original code

        public string Buffer
        {
            get { return _buffer; }
        }
        public bool BackSpace
        {
            get
            {
                return _backSpace;
            }
        }
        public bool EnterKey
        {
            get
            {
                return _enterKey;
            }
        }
        public void Reset()
        {
            _buffer = "";
            _backSpace = false;
            _enterKey = false;
        }

        public enum HookId
        {
            // Types of hook that can be installed using the SetWindwsHookEx function.
            WH_CALLWNDPROC = 4,
            WH_CALLWNDPROCRET = 12,
            WH_CBT = 5,
            WH_DEBUG = 9,
            WH_FOREGROUNDIDLE = 11,
            WH_GETMESSAGE = 3,
            WH_HARDWARE = 8,
            WH_JOURNALPLAYBACK = 1,
            WH_JOURNALRECORD = 0,
            WH_KEYBOARD = 2,
            WH_KEYBOARD_LL = 13,
            WH_MAX = 11,
            WH_MAXHOOK = WH_MAX,
            WH_MIN = -1,
            WH_MINHOOK = WH_MIN,
            WH_MOUSE_LL = 14,
            WH_MSGFILTER = -1,
            WH_SHELL = 10,
            WH_SYSMSGFILTER = 6,
        };
        public enum WindowMessage
        {
            // Window message types.
            WM_KEYDOWN = 0x100,
            WM_KEYUP = 0x101,
            WM_CHAR = 0x102,
        };

        // A delegate used to create a hook callback.
        public delegate int GetMsgProc(int nCode, int wParam, ref Message msg);

        /// <summary>
        /// Install an application-defined hook procedure into a hook chain.
        /// </summary>
        /// <param name="idHook">Specifies the type of hook procedure to be installed.</param>
        /// <param name="lpfn">Pointer to the hook procedure.</param>
        /// <param name="hmod">Handle to the DLL containing the hook procedure pointed to by the lpfn parameter.</param>
        /// <param name="dwThreadId">Specifies the identifier of the thread with which the hook procedure is to be associated.</param>
        /// <returns>If the function succeeds, the return value is the handle to the hook procedure. Otherwise returns 0.</returns>
        [DllImport("user32.dll", EntryPoint = "SetWindowsHookExA")]
        public static extern IntPtr SetWindowsHookEx(HookId idHook, GetMsgProc lpfn, IntPtr hmod, int dwThreadId);

        /// <summary>
        /// Removes a hook procedure installed in a hook chain by the SetWindowsHookEx function. 
        /// </summary>
        /// <param name="hHook">Handle to the hook to be removed. This parameter is a hook handle obtained by a previous call to SetWindowsHookEx.</param>
        /// <returns>If the function fails, the return value is zero. To get extended error information, call GetLastError.</returns>
        [DllImport("user32.dll")]
        public static extern int UnhookWindowsHookEx(IntPtr hHook);

        /// <summary>
        /// Passes the hook information to the next hook procedure in the current hook chain.
        /// </summary>
        /// <param name="hHook">Ignored.</param>
        /// <param name="ncode">Specifies the hook code passed to the current hook procedure.</param>
        /// <param name="wParam">Specifies the wParam value passed to the current hook procedure.</param>
        /// <param name="lParam">Specifies the lParam value passed to the current hook procedure.</param>
        /// <returns>This value is returned by the next hook procedure in the chain.</returns>
        [DllImport("user32.dll")]
        public static extern int CallNextHookEx(int hHook, int ncode, int wParam, ref Message lParam);

        /// <summary>
        /// Translates virtual-key messages into character messages.
        /// </summary>
        /// <param name="lpMsg">Pointer to an Message structure that contains message information retrieved from the calling thread's message queue.</param>
        /// <returns>If the message is translated (that is, a character message is posted to the thread's message queue), the return value is true.</returns>
        [DllImport("user32.dll")]
        public static extern bool TranslateMessage(ref Message lpMsg);


        /// <summary>
        /// Retrieves the thread identifier of the calling thread.
        /// </summary>
        /// <returns>The thread identifier of the calling thread.</returns>
        [DllImport("kernel32.dll")]
        public static extern int GetCurrentThreadId();

        // Handle for the created hook.
        private readonly IntPtr HookHandle;

        private readonly GetMsgProc ProcessMessagesCallback;

        public KeyboardHookInput()
        {
            // Create the delegate callback:
            this.ProcessMessagesCallback = new GetMsgProc(ProcessMessages);
            // Create the keyboard hook:
            this.HookHandle = SetWindowsHookEx(HookId.WH_KEYBOARD, this.ProcessMessagesCallback, IntPtr.Zero, GetCurrentThreadId());
        }

        public void Dispose()
        {
            // Remove the hook.
            if (HookHandle != IntPtr.Zero) UnhookWindowsHookEx(HookHandle);
        }

        // comments found in this region are all from the original author: Darg.
        private int ProcessMessages(int nCode, int wParam, ref Message msg)
        {
            // Check if we must process this message (and whether it has been retrieved via GetMessage):
            if (nCode == 0 && wParam == 1)
            {
                // We need character input, so use TranslateMessage to generate WM_CHAR messages.
                TranslateMessage(ref msg);

                // If it's one of the keyboard-related messages, raise an event for it:
                switch ((WindowMessage)msg.Msg)
                {
                    case WindowMessage.WM_CHAR:
                        this.OnKeyPress(new KeyPressEventArgs((char)msg.WParam));
                        break;
                    case WindowMessage.WM_KEYDOWN:
                        this.OnKeyDown(new KeyEventArgs((Keys)msg.WParam));
                        break;
                    case WindowMessage.WM_KEYUP:
                        this.OnKeyUp(new KeyEventArgs((Keys)msg.WParam));
                        break;
                }
            }
            // Call next hook in chain:
            return CallNextHookEx(0, nCode, wParam, ref msg);
        }

        public event KeyEventHandler KeyUp;
        protected virtual void OnKeyUp(KeyEventArgs e)
        {
            if (KeyUp != null) KeyUp(this, e);
        }

        public event KeyEventHandler KeyDown;
        protected virtual void OnKeyDown(KeyEventArgs e)
        {
            if (KeyDown != null) KeyDown(this, e);
        }

        public event KeyPressEventHandler KeyPress;
        protected virtual void OnKeyPress(KeyPressEventArgs e)
        {
            if (KeyPress != null) KeyPress(this, e);
            if (e.KeyChar.GetHashCode().ToString() == "524296")
            {
                _backSpace = true;
            }
            else if (e.KeyChar == (char)Keys.Enter)
            {
                _enterKey = true;
            }
            else
            {
                _buffer += e.KeyChar;
            }
        }
    }
}

Answer 1

A Windows Hook is a pretty nasty way of getting at all the keypresses, and should be an absolute last resort.

Try installing a Message Filter into your application, which can watch for all the keyboard messages that are sent to your application (WM_KEYPRESS, KEYUP, KEYDOWN, etc) without interfering with other applications. A filter will also allow you to stop any messages reaching any forms in your application if you wish.