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Check if non-modifier keys are in pressed state during mouse events

You have several options:

Option 1: Add custom message filter to your application:

private KeyMessageFilter _filter = new

private void Form1_Load(object sender, EventArgs

public class KeyMessageFilter : IMessageFilter
    private Dictionary<Keys, bool> _keyTable
= new Dictionary<Keys, bool>();

    public Dictionary<Keys, bool> KeyTable
        get { return _keyTable; }
        private set { _keyTable = value; }

    public bool IsKeyPressed()
        return _keyPressed; 

    public bool IsKeyPressed(Keys k)
        bool pressed = false;

        if (KeyTable.TryGetValue(k, out pressed))
            return pressed;                  

        return false; 

    private const int WM_KEYDOWN = 0x0100;

    private const int WM_KEYUP = 0x0101;

    private bool _keyPressed = false;

    public bool PreFilterMessage(ref Message m)
        if (m.Msg == WM_KEYDOWN)
            KeyTable[(Keys)m.WParam] = true;

            _keyPressed = true;

        if (m.Msg == WM_KEYUP)
            KeyTable[(Keys)m.WParam] = false;

            _keyPressed = false;

        return false;        

Option 2: Use GetKeyState API function as linked before:

using System;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace MouseKeyboardStateTest
  public abstract class Keyboard
    private enum KeyStates
      None = 0,
      Down = 1,
      Toggled = 2

    [DllImport("user32.dll", CharSet =
CharSet.Auto, ExactSpelling = true)]
    private static extern short GetKeyState(int

    private static KeyStates GetKeyState(Keys key)
      KeyStates state = KeyStates.None;

      short retVal = GetKeyState((int)key);

      //If the high-order bit is 1, the key is
      //otherwise, it is up.
      if ((retVal & 0x8000) == 0x8000)
        state |= KeyStates.Down;

      //If the low-order bit is 1, the key is
      if ((retVal & 1) == 1)
        state |= KeyStates.Toggled;

      return state;

    public static bool IsKeyDown(Keys key)
      return KeyStates.Down == (GetKeyState(key)
& KeyStates.Down);

    public static bool IsKeyToggled(Keys key)
      return KeyStates.Toggled ==
(GetKeyState(key) & KeyStates.Toggled);

Option 3: Handle KeyDown And KeyUp events by yourself. It's not best approach but for small application would be nice.

Categories : C#

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