MATLAB Example Code - isKeyPressed

Note: The function requires MATLAB 7.4 or greater for the KeyReleaseFCN? functionality. Attempting to run the function on any version earlier than 7.4 will result in an error.

The isKeyPressed function checks to see if a certain key is pressed. For simplicity, a string is used for the arrow keys (upArrow, downArrow, leftArrow, rightArrow) as opposed to using the nominal control characters normally associated with the arrow keys. Single keys may also be checked by passing their values to the function.

Examples

Check to see if the up arrow key is being pressed

if isKeyPressed('upArrow') == 1
    % React to the fact that the upArrow key is currently being pressed
end

if isKeyPressed('A') == 1
    % React to the fact that the A key is currently being pressed
end

Source Code

function [keyPressed]= isKeyPressed(keyToCheck)
%   usage:      isKeyPressed(keyToCheck)
%   purpose:   Tests to see if a key is being pressed
    global gCurrentKeyPress;

   currentKey = gCurrentKeyPress;

% Is there anything to process?
   if isempty(currentKey) == 1;
      keyPressed = 0; 
      return;
   end

% Default is 0 unless we find otherwise
   keyPressed = 0;

% Quick check of an exact match
   if keyToCheck == currentKey
      currentKey= 1;
   else 
% Exceptions using string checks for the string mappings of arrows
%   (our mapping, not MATLAB's)
      if strcmp(keyToCheck, 'upArrow') == 1;
         if currentKey == 30
            keyPressed = 1
         end
      end  
      if strcmp(keyToCheck, 'downArrow') == 1;
         if currentKey == 31
            keyPressed = 1
         end
      end  
      if strcmp(keyToCheck, 'rightArrow') == 1;
         if currentKey == 29
            keyPressed = 1
         end
      end  
      if strcmp(keyToCheck, 'leftArrow') == 1;
         if currentKey == 28
            keyPressed = 1
         end
      end  
   end
end

Other Notes

• It does not prevent the capture of multiple key strokes, i.e. if the key is still pressed multiple calls to isKeyPressed will still show that it is pressed.

Related Code / Code Dependencies

• Dependency: keyHandlerPress - Handler for when keys are pressed by the user
• Dependency: keyHandlerRelease - Handler for when keys are released by the user