Detect if any key is pressed in C# (not A, B, but any)

Question

Hi,

[EDIT 3] I kind of "solved it" by at using the "strange" version. At least for the most important keys. It is suffient for my case, where I want to check that ALT and ALT+A are not the same (thereby making sure A is not pressed). Not perfect, but already to much time for such a tiny problem. Thanks for all the answers anyway... [EDIT 3]

[EDIT 4] Solved it much cleaner thanks to 280Z28 [/EDIT 4]

I know how to check for modifier keys and how to test for a single key. The problem is, I want to check if any key is pressed. The following approach seems "strange" :-)

WPF Application written in C#

if (Keyboard.IsKeyDown(Key.A)) return true;
if (Keyboard.IsKeyDown(Key.B)) return true;
if (Keyboard.IsKeyDown(Key.C)) return true;

I know it is an enum, so I thought about a loop, but what is the "biggest number" to use. And is this possible? btw, its a very special case, normally I would use an event, but in this case I have to do it this way. Unfortunatily, the there is no "list" Keyboard.CurrentlyDownKeys. At least I didnt see it.

Thanks, Chris

EDIT: Ok, because it seems to be a bigger deal, here the reason for this: I have defined a "KeySet" which serves as DictionaryKey for custom functions. If anybody clicks on an element, the wrapper iterates through the dictionary and checks if any of the predefined "Keysets" is active.

This allows me to define simple triggers, like e.g. Run this function if ALT+A+B is pressed. Another option is e.g. Run this function if ALT+STRG+A is pressed (during a mouse click on a WPF element).

The only "problem" with the current implementation, if I define a Keyset which does NOT contain any REAL keys, like run if ALT is pressed, it is also triggered if ALT+A is pressed. Oh, while writing this, I realize that there is another problem. ALT+A+B would currently also trigger if ALT+A+B+C is pressed.

Perhaps my approach is wrong, and I should create a "static key tracker" and compare the keyset to its values (aquired via events).. I will give this a try.

EDIT 2 This is not working, at least not in a simple way. I need an FrameworkElement to attach to KeyDown, but I do not have it in a static constructor. And I am not interested in KeyDownEvents of a certain element, but "globally"...I think I juts postpone this problem, its not that important. Still, if anybody knows a better of different approach...

So long, for anyone who cares, here some code:

    public class KeyModifierSet
{
    internal readonly HashSet<Key> Keys = new HashSet<Key>();
    internal readonly HashSet<ModifierKeys> MKeys = new HashSet<ModifierKeys>();

    public override int GetHashCode()
    {
        int hash = Keys.Count + MKeys.Count;
        foreach (var t in Keys)
        {
            hash *= 17;
            hash = hash + t.GetHashCode();
        }
        foreach (var t in MKeys)
        {
            hash *= 19;
            hash = hash + t.GetHashCode();
        }
        return hash;
    }

    public override bool Equals(object obj)
    {
        return Equals(obj as KeyModifierSet);
    }
    public bool Equals(KeyModifierSet other)
    {
        // Check for null
        if (ReferenceEquals(other, null))
            return false;

        // Check for same reference
        if (ReferenceEquals(this, other))
            return true;

        // Check for same Id and same Values
        return Keys.SetEquals(other.Keys) && MKeys.SetEquals(other.MKeys);
    }

    public bool IsActive()
    {
        foreach (var k in Keys)
            if (Keyboard.IsKeyUp(k)) return false;

        if ((Keys.Count == 0) && !Keyboard.IsKeyDown(Key.None)) return false;


        foreach (var k in MKeys)
            if ((Keyboard.Modifiers & k) == 0) return false;

        if ((MKeys.Count == 0) && Keyboard.Modifiers > 0) return false;

        return true;
    }


    public KeyModifierSet(ModifierKeys mKey)
    {
        MKeys.Add(mKey);
    }
    public KeyModifierSet()
    {

    }
    public KeyModifierSet(Key key)
    {
        Keys.Add(key);
    }
    public KeyModifierSet(Key key, ModifierKeys mKey)
    {
        Keys.Add(key);
        MKeys.Add(mKey);
    }
    public KeyModifierSet Add(Key key)
    {
        Keys.Add(key);
        return this;
    }
    public KeyModifierSet Add(ModifierKeys key)
    {
        MKeys.Add(key);
        return this;
    }
}

Answer 1

Where is this code running from? Is it in an event handler? Many forms and controls will fire a KeyPress event as well as a KeyDown event. You may want to look into those events and set your flag to true when one of them occurs. You'd also have to listen for the corresponding event that tells you when the key is released (KeyUp, also, I think).

Answer 2

normally I would use an event

You should still be using an event, preferably KeyDown since you don't mind what key is pressed, if you are programming on windows. If not, you could use something like Console.ReadLine();.

edit: If you are looking for something like

if (Keyboard.IsKeyDown(Key.AnyKey)) return true;

then you must be joking...

edit 2: Well, the approach of your logger is interesting, but I think that you are reinventing the wheel. All programming languages provides some way to handle wich key was pressed, when this can be known. In C# for Windows, this is done using events. Besides, I think you won't be able to handle this kind of things by yourself in .NET, since you need to access some system functions from the Win32 API, and AFAIK you aren't allowed to do this (at least easily...) in managed code. Some solution would be to create a HOOK and send messages from there to your application, but I don't know how to do this in C#. This was the way in Delphi, where I have more experience.

Answer 3

http://sourceforge.net/projects/keystate/ shows "special" keys. Otherwise I think you're just going to have to monitor them. SOunds like you want to do this systemwide? What are you trying to accomplish?

Answer 4

You can increment a counter for each keydown event, and decrement it for each keyup event. When the counter is zero, no keys are down.

Answer 5

See this question : Capture KeyDown Event in WPF

Answer 6

[DllImport("user32.dll", EntryPoint = "GetKeyboardState", SetLastError = true)]
private static extern bool NativeGetKeyboardState([Out] byte[] keyStates);

private static bool GetKeyboardState(byte[] keyStates)
{
    if (keyStates == null)
        throw new ArgumentNullException("keyState");
    if (keyStates.Length != 256)
        throw new ArgumentException("The buffer must be 256 bytes long.", "keyState");
    return NativeGetKeyboardState(keyStates);
}

private static byte[] GetKeyboardState()
{
    byte[] keyStates = new byte[256];
    if (!GetKeyboardState(keyStates))
        throw new Win32Exception(Marshal.GetLastWin32Error());
    return keyStates;
}

private static bool AnyKeyPressed()
{
    byte[] keyState = GetKeyboardState();
    // skip the mouse buttons
    return keyState.Skip(8).Any(state => (state & 0x80) != 0);
}