Question

I made an application that needs to handle specific keyboard presses even when the window is not active, now I have this and it works great; however the handled keys are still being propagated to windows (not sure if my app is handling them first, so I may be backwards about that).

Is there any way to have it so my app can handle the key presses I want but not have the keys be sent to the current application/windows.

EX) I have my app open in the background monitoring the number pad for presses, every time I press a number key on the number pad I want to add that number to a text box for display purposes. Now I have chrome open and have the cursor in the address bar, I want to be able to press the number keys while having my app handle them but not having them show up in chromes address bar.

Thanks.

This is basically a very simplistic key logger.

EDIT)
Keyboard Hook

#endregion
using System;
using System.Text;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using System.Windows.Forms;   

public class GlobalKeyboardHook
{
[DllImport("user32.dll")]
static extern int CallNextHookEx(IntPtr hhk, int code, int wParam, ref keyBoardHookStruct lParam);
[DllImport("user32.dll")]
static extern IntPtr SetWindowsHookEx(int idHook, LLKeyboardHook callback, IntPtr hInstance, uint theardID);
[DllImport("user32.dll")]
static extern bool UnhookWindowsHookEx(IntPtr hInstance);
[DllImport("kernel32.dll")]
static extern IntPtr LoadLibrary(string lpFileName);

public delegate int LLKeyboardHook(int Code, int wParam, ref keyBoardHookStruct lParam);

public struct keyBoardHookStruct
{
    public int vkCode;
    public int scanCode;
    public int flags;
    public int time;
    public int dwExtraInfo;
}

const int WH_KEYBOARD_LL = 13;
const int WM_KEYDOWN = 0x0100;
const int WM_KEYUP = 0x0101;
const int WM_SYSKEYDOWN = 0x0104;
const int WM_SYSKEYUP = 0x0105;

LLKeyboardHook llkh;
public List<Keys> HookedKeys = new List<Keys>();

IntPtr Hook = IntPtr.Zero;

public event KeyEventHandler KeyDown;
public event KeyEventHandler KeyUp;

public GlobalKeyboardHook()
{
    llkh = new LLKeyboardHook(HookProc);
    hook();
}
~GlobalKeyboardHook()
{ unhook(); }

public void hook()
{
    IntPtr hInstance = LoadLibrary("User32");
    Hook = SetWindowsHookEx(WH_KEYBOARD_LL, llkh, hInstance, 0);
}

public void unhook()
{
    UnhookWindowsHookEx(Hook);
}

public int HookProc(int Code, int wParam, ref keyBoardHookStruct lParam)
{
    if (Code >= 0)
    {
        Keys key = (Keys)lParam.vkCode;
        if (HookedKeys.Contains(key))
        {
            KeyEventArgs kArg = new KeyEventArgs(key);
            if ((wParam == WM_KEYDOWN || wParam == WM_SYSKEYDOWN) && (KeyDown != null))
                KeyDown(this, kArg);
            else if ((wParam == WM_KEYUP || wParam == WM_SYSKEYUP) && (KeyUp != null))
                KeyUp(this, kArg);
            if (kArg.Handled)
                return 1;
        }
    }
    return CallNextHookEx(Hook, Code, wParam, ref lParam);
}

}

Usage of GlobalKeyboardHook

GlobalKeyboardHook gHook;
private void Form1_Load(object sender, EventArgs e)
{
   gHook = new GlobalKeyboardHook(); // Create a new GlobalKeyboardHook
   // Declare a KeyDown Event
   gHook.KeyDown += new KeyEventHandler(gHook_KeyDown);
   // Add the keys you want to hook to the HookedKeys list
   foreach (Keys key in Enum.GetValues(typeof(Keys)))
       gHook.HookedKeys.Add(key);
}

// Handle the KeyDown Event
public void gHook_KeyDown(object sender, KeyEventArgs e)
{
   textBox1.Text += ((char)e.KeyValue).ToString();
}

private void button1_Click(object sender, EventArgs e)
{
   gHook.hook();
}

private void button2_Click(object sender, EventArgs e)
{
   gHook.unhook();
}

private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
   gHook.unhook();
}

Answer 1

In your hookProc, you must not call return CallNextHookEx(Hook, Code, wParam, ref lParam); if you dont want the WM_KEYS to propagate.

If you do call CallNextHookEx, the messages will be propagated.

Btw, you are aware that you are using a Global hook, and not a thread specific hook ? So you are capturing ALL key presses, and not only the ones relative to your app.