Roy Triesscheijn’s Weblog

In the standard XNA libraries, there is no method that deals with converting keyboard input to text. There are several methods on the Internet, but most of them are pretty incomplete or extremely slow. I found one solution, which was pretty complete, but it used a gigantic “if-then-else if…” to check every key to see if it was pressed. This makes for an extremely slow process (Still O(c) where c is constant), but having the computer look trough 60 if-statements every frame is a bit of a waste.

After I couldn’t find anything else to my liking I decided to create my own method. I used GetPressedKeys() to get the pressed keys. If keys are pressed I take the first one (if a users presses multiple keys at once, except modifier keys like shift, it’s rubbish anyway). And throw that one in a switch, which branches to the correct character immediately (in contrast to an if-then-else-if construction). I’ve tried modeled the code the same as TryParse, so a bool is returned to show that we either converted a character, or not. And via the out keyword, we pass the found character.

(Note: some of the ‘oem’-keys might not register when pressing shift, see here for a bit more in depth info about this known bug in XNA’s Keyboard api).

 /// <summary>
        /// Tries to convert keyboard input to characters and prevents repeatedly returning the
        /// same character if a key was pressed last frame, but not yet unpressed this frame.
        /// </summary>
        /// <param name="keyboard">The current KeyboardState</param>
        /// <param name="oldKeyboard">The KeyboardState of the previous frame</param>
        /// <param name="key">When this method returns, contains the correct character if conversion succeeded.
        /// Else contains the null, (000), character.</param>
        /// <returns>True if conversion was successful</returns>
        public static bool TryConvertKeyboardInput(KeyboardState keyboard, KeyboardState oldKeyboard, out char key)
        {
            Keys[] keys = keyboard.GetPressedKeys();
            bool shift = keyboard.IsKeyDown(Keys.LeftShift) || keyboard.IsKeyDown(Keys.RightShift);            

            if(keys.Length > 0 && !oldKeyboard.IsKeyDown(keys[0]))
            {
                switch (keys[0])
                {
                    //Alphabet keys
                    case Keys.A: if (shift) { key = 'A'; } else { key = 'a'; } return true;
                    case Keys.B: if (shift) { key = 'B'; } else { key = 'b'; } return true;
                    case Keys.C: if (shift) { key = 'C'; } else { key = 'c'; } return true;
                    case Keys.D: if (shift) { key = 'D'; } else { key = 'd'; } return true;
                    case Keys.E: if (shift) { key = 'E'; } else { key = 'e'; } return true;
                    case Keys.F: if (shift) { key = 'F'; } else { key = 'f'; } return true;
                    case Keys.G: if (shift) { key = 'G'; } else { key = 'g'; } return true;
                    case Keys.H: if (shift) { key = 'H'; } else { key = 'h'; } return true;
                    case Keys.I: if (shift) { key = 'I'; } else { key = 'i'; } return true;
                    case Keys.J: if (shift) { key = 'J'; } else { key = 'j'; } return true;
                    case Keys.K: if (shift) { key = 'K'; } else { key = 'k'; } return true;
                    case Keys.L: if (shift) { key = 'L'; } else { key = 'l'; } return true;
                    case Keys.M: if (shift) { key = 'M'; } else { key = 'm'; } return true;
                    case Keys.N: if (shift) { key = 'N'; } else { key = 'n'; } return true;
                    case Keys.O: if (shift) { key = 'O'; } else { key = 'o'; } return true;
                    case Keys.P: if (shift) { key = 'P'; } else { key = 'p'; } return true;
                    case Keys.Q: if (shift) { key = 'Q'; } else { key = 'q'; } return true;
                    case Keys.R: if (shift) { key = 'R'; } else { key = 'r'; } return true;
                    case Keys.S: if (shift) { key = 'S'; } else { key = 's'; } return true;
                    case Keys.T: if (shift) { key = 'T'; } else { key = 't'; } return true;
                    case Keys.U: if (shift) { key = 'U'; } else { key = 'u'; } return true;
                    case Keys.V: if (shift) { key = 'V'; } else { key = 'v'; } return true;
                    case Keys.W: if (shift) { key = 'W'; } else { key = 'w'; } return true;
                    case Keys.X: if (shift) { key = 'X'; } else { key = 'x'; } return true;
                    case Keys.Y: if (shift) { key = 'Y'; } else { key = 'y'; } return true;
                    case Keys.Z: if (shift) { key = 'Z'; } else { key = 'z'; } return true;

                    //Decimal keys
                    case Keys.D0: if (shift) { key = ')'; } else { key = '0'; } return true;
                    case Keys.D1: if (shift) { key = '!'; } else { key = '1'; } return true;
                    case Keys.D2: if (shift) { key = '@'; } else { key = '2'; } return true;
                    case Keys.D3: if (shift) { key = '#'; } else { key = '3'; } return true;
                    case Keys.D4: if (shift) { key = '$'; } else { key = '4'; } return true;
                    case Keys.D5: if (shift) { key = '%'; } else { key = '5'; } return true;
                    case Keys.D6: if (shift) { key = '^'; } else { key = '6'; } return true;
                    case Keys.D7: if (shift) { key = '&'; } else { key = '7'; } return true;
                    case Keys.D8: if (shift) { key = '*'; } else { key = '8'; } return true;
                    case Keys.D9: if (shift) { key = '('; } else { key = '9'; } return true;

                    //Decimal numpad keys
                    case Keys.NumPad0: key = '0'; return true;
                    case Keys.NumPad1: key = '1'; return true;
                    case Keys.NumPad2: key = '2'; return true;
                    case Keys.NumPad3: key = '3'; return true;
                    case Keys.NumPad4: key = '4'; return true;
                    case Keys.NumPad5: key = '5'; return true;
                    case Keys.NumPad6: key = '6'; return true;
                    case Keys.NumPad7: key = '7'; return true;
                    case Keys.NumPad8: key = '8'; return true;
                    case Keys.NumPad9: key = '9'; return true;

                    //Special keys
                    case Keys.OemTilde: if (shift) { key = '~'; } else { key = '`'; } return true;
                    case Keys.OemSemicolon: if (shift) { key = ':'; } else { key = ';'; } return true;
                    case Keys.OemQuotes: if (shift) { key = '"'; } else { key = '\''; } return true;
                    case Keys.OemQuestion: if (shift) { key = '?'; } else { key = '/'; } return true;
                    case Keys.OemPlus: if (shift) { key = '+'; } else { key = '='; } return true;
                    case Keys.OemPipe: if (shift) { key = '|'; } else { key = '\\'; } return true;
                    case Keys.OemPeriod: if (shift) { key = '>'; } else { key = '.'; } return true;
                    case Keys.OemOpenBrackets: if (shift) { key = '{'; } else { key = '['; } return true;
                    case Keys.OemCloseBrackets: if (shift) { key = '}'; } else { key = ']'; } return true;
                    case Keys.OemMinus: if (shift) { key = '_'; } else { key = '-'; } return true;
                    case Keys.OemComma: if (shift) { key = '<'; } else { key = ','; } return true;
                    case Keys.Space: key = ' '; return true;
                }
            }

            key = (char)0;
            return false;
        }

I hope you enjoy this code, feel free to use it, but if you do please post a thank you message here or something like that. As usual tips, tricks, comments and improvements are welcome!