C# How to translate virtual keycode to char?

Question

I am trying to map a virtual keycode to a char.

My code uses ProcessCmdKey to listen to WM_KEYDOWN which gives me access to the key pressed. For example, when I press single quote I get a key of 222 which I want to have it mapped to keychar 39 which represents... you guessed it... single quote.

My dev context is: - .net Framework 2.0 - UserControl placed in a lot of places

Do you know the answer to the question?

Answer 1

Isn't that what the System.Windows.Form.KeysConverter class is for?

KeysConverter kc = new KeysConverter();
string keyChar = kc.ConvertToString(keyData);

Answer 2

Yes, I did use the MapVirtualKey method. But I was expecting more details on how to use it: what DllImport directive to use, what enum is specific for mapping to characters, etc.

I don't like these answers where you google for like 5 seconds and then just suggest a solution: the real challenge is to put all the pieces together and not have to waste your time with tons of sample-less MSDN pages or other coding forums in order to get your answer. No offense plinth, but your answer (even good) was worhtless since I had this answer even before posting my question on the forum!

So there you go, I am going to post what I was looking for - an out-of-the-box C# solution:

1- Place this directive inside your class:

[DllImport("user32.dll")]
static extern int MapVirtualKey(uint uCode, uint uMapType);

2- Retrieve your char like this:

  protected override bool ProcessCmdKey(ref Message msg, Keys keyData)      
  {
     const int WM_KEYDOWN = 0x100;

     if (msg.Msg == WM_KEYDOWN)
     {            
        // 2 is used to translate into an unshifted character value 
        int nonVirtualKey = MapVirtualKey((uint)keyData, 2);

        char mappedChar = Convert.ToChar(nonVirtualKey);
     }

     return base.ProcessCmdKey(ref msg, keyData);
  }

Thanks for caring... and enjoy!

Answer 3

I was looking for something similar but I needed the character mapped to the current keyboard layout. Since none of the above answers fulfilled my requirements, here is what I came up with.

        public string KeyCodeToUnicode(Keys key)
        {
            byte[] keyboardState = new byte[255];
            bool keyboardStateStatus = GetKeyboardState(keyboardState);

            if (!keyboardStateStatus)
            {
                return "";
            }

            uint virtualKeyCode = (uint)key;
            uint scanCode = MapVirtualKey(virtualKeyCode, 0);
            IntPtr inputLocaleIdentifier = GetKeyboardLayout(0);

            StringBuilder result = new StringBuilder();
            ToUnicodeEx(virtualKeyCode, scanCode, keyboardState, result, (int)5, (uint)0, inputLocaleIdentifier);

            return result.ToString();
        }

        [DllImport("user32.dll")]
        static extern bool GetKeyboardState(byte[] lpKeyState);

        [DllImport("user32.dll")]
        static extern uint MapVirtualKey(uint uCode, uint uMapType);

        [DllImport("user32.dll")]
        static extern IntPtr GetKeyboardLayout(uint idThread);

        [DllImport("user32.dll")]
        static extern int ToUnicodeEx(uint wVirtKey, uint wScanCode, byte[] lpKeyState, [Out, MarshalAs(UnmanagedType.LPWStr)] StringBuilder pwszBuff, int cchBuff, uint wFlags, IntPtr dwhkl);

Answer 4

After reading and testing some of the answers provided, I thought I'd suggest an alternative.

As mentioned by MM, System.Windows.KeysConverter does not provide a character representation of the key but rather the enum's name, e.g. "Enter" instead of '\n'.

The MapVirtualKey method suggested by Horas, in answer to his own question, is a good starting point, but still does not support either capslock, or characters entered with the shift key, e.g. '!', '$' and '>'.

An alternative to the MapVirtualKey method, that I am using, is an extension method for the Keys class:

public static char ToChar(this Keys key)
{
    char c = '\0';
    if((key >= Keys.A) && (key <= Keys.Z))
    {
        c = (char)((int)'a' + (int)(key - Keys.A));
    }

    else if((key >= Keys.D0) && (key <= Keys.D9))
    {
        c = (char)((int)'0' + (int)(key - Keys.D0));
    }

    return c;
}

The method shown above will provide support for alphanumeric characters. Support for additional characters could be implemented with either a switch statement or lookup table.

Answer 5

I've just written an improvement of Ivan Petrov answer to display a string representation of pressed key combinations in WPF, see my code below:

public static string GetKeyString(Key key, ModifierKeys modifiers)
{
    string result = "";
    if (key != Key.None)
    {
        // Setup modifiers
        if (modifiers.HasFlag(ModifierKeys.Control))
            result += "Ctrl + ";
        if (modifiers.HasFlag(ModifierKeys.Alt))
            result += "Alt + ";
        if (modifiers.HasFlag(ModifierKeys.Shift))
            result += "Shift + ";
        // Get string representation
        string keyStr = key.ToString();
        int keyInt = (int)key;
        // Numeric keys are returned without the 'D'
        if (key >= Key.D0 && key <= Key.D9)
            keyStr = char.ToString((char)(key - Key.D0 + '0'));
        // Char keys are returned directly
        else if (key >= Key.A && key <= Key.Z)
            keyStr = char.ToString((char)(key - Key.A + 'A'));
        // If the key is a keypad operation (Add, Multiply, ...) or an 'Oem' key, P/Invoke
        else if ((keyInt >= 84 && keyInt <= 89) || keyInt >= 140)
            keyStr = KeyCodeToUnicode(key);
        result += keyStr;
    }
    return result;
}

private static string KeyCodeToUnicode(Key key)
{
    byte[] keyboardState = new byte[255];
    bool keyboardStateStatus = GetKeyboardState(keyboardState);

    if (!keyboardStateStatus)
    {
        return "";
    }

    uint virtualKeyCode = (uint)KeyInterop.VirtualKeyFromKey(key);
    uint scanCode = MapVirtualKey(virtualKeyCode, 0);
    IntPtr inputLocaleIdentifier = GetKeyboardLayout(0);

    StringBuilder result = new StringBuilder();
    ToUnicodeEx(virtualKeyCode, scanCode, new byte[255], result, (int)5, (uint)0, inputLocaleIdentifier);

    return result.ToString();
}

[DllImport("user32.dll")]
static extern bool GetKeyboardState(byte[] lpKeyState);

[DllImport("user32.dll")]
static extern uint MapVirtualKey(uint uCode, uint uMapType);

[DllImport("user32.dll")]
static extern IntPtr GetKeyboardLayout(uint idThread);

[DllImport("user32.dll")]
static extern int ToUnicodeEx(uint wVirtKey, uint wScanCode, byte[] lpKeyState, [Out, MarshalAs(UnmanagedType.LPWStr)] StringBuilder pwszBuff, int cchBuff, uint wFlags, IntPtr dwhkl);

Answer 6

KeysConverter gets the key name not the keys "text" ex: "Num2" instead of "2" MapVirtualKey will work for english but for non-english chars documentation states using MapVirtualKeyEx but that requires a locale Identifier that identifier is loaded by LoadKeyBoardLayout which requires a culture id constant but then after finding the correct id values it didn't work as i tried it so finally i dumped the whole thing

Answer 7

If you are using WPF (I didn't try it with WinForms), there is a very simple solution that returns directly the pressed char, the TextInput Event of Window.

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        TextInput += MainWindow_TextInput;
    }

    private void MainWindow_TextInput(object sender, System.Windows.Input.TextCompositionEventArgs e)
    {
        txtInput.Text += e.Text;
    }
}