how to capture the '#' character on different locale keyboards in WPF/C#?

Question

My WPF application handles keyboard presses and specifically the # and * character as it is a VoIP phone.

I have a bug though with international keyboards, and in particular the British english keyboard. Normally I listen for the 3 key and if the shift key modifier is down we fire off an event to do stuff. However on the British keyboard this is the '£' character. I found that the UK english keyboard has a dedicated key for '#'. Obviously we could just listen for that particular key, but that doesn't solve the case for US english which is shift-3 and all the countless other keyboards that put it somewhere else.

Long story short, how do I listen for a particular character from a key press, whether it's a key combo or single key and react to it?

Answer 1

The function below, GetCharFromKey(Key key) will do the trick.

It uses a series of win32 calls to decode the key pressed:

1. get the virtual key from WPF key

2. get the scan code from the virtual key

3. get your unicode character

This old post describes it in a bit more detail.

      public enum MapType : uint       {          MAPVK_VK_TO_VSC = 0x0,          MAPVK_VSC_TO_VK = 0x1,          MAPVK_VK_TO_CHAR = 0x2,          MAPVK_VSC_TO_VK_EX = 0x3,       }        [DllImport("user32.dll")]       public static extern int ToUnicode(           uint wVirtKey,           uint wScanCode,           byte[] lpKeyState,           [Out, MarshalAs(UnmanagedType.LPWStr, SizeParamIndex = 4)]              StringBuilder pwszBuff,           int cchBuff,           uint wFlags);        [DllImport("user32.dll")]       public static extern bool GetKeyboardState(byte[] lpKeyState);        [DllImport("user32.dll")]       public static extern uint MapVirtualKey(uint uCode, MapType uMapType);        public static char GetCharFromKey(Key key)       {          char ch = ' ';           int virtualKey = KeyInterop.VirtualKeyFromKey(key);          byte[] keyboardState = new byte[256];          GetKeyboardState(keyboardState);           uint scanCode = MapVirtualKey((uint)virtualKey, MapType.MAPVK_VK_TO_VSC);          StringBuilder stringBuilder = new StringBuilder(2);           int result = ToUnicode((uint)virtualKey, scanCode, keyboardState, stringBuilder, stringBuilder.Capacity, 0);          switch (result)          {             case -1:                 break;             case 0:                 break;             case 1:                {                   ch = stringBuilder[0];                   break;                }             default:                {                   ch = stringBuilder[0];                   break;                }          }          return ch;       } 

Answer 2

I found a helpful solution in this post: http://www.codewrecks.com/blog/index.php/2008/05/06/wpf-convert-systemwindowsinputkey-to-char-or-string-2/

There is another event TextInput or PreviewTextInput which gives the character as string instead of the Key :).