MATLAB: Parallel Problem: Get keyboard input in 60 sec, otherwise jump out

parallel computing

Hi to all, I recently encountered a problem. I want to get the keyboard input and read it and put something on the screen if the user puts a cerntain key such as 'q'. However, if the user doesn't put in anything in 20 sec, I want the time counter to start again. This procedure loops over for 60 times.

Can anyone help me with this? Thank you very much!

Best Answer

Shijia, you can do something like this using callbacks. Here's an example using figure callbacks. Save it as myFunction.m and see if you can follow what it does:

function myFunction
figure('KeyPressFcn',@kp);
ticCount = 0;
lastTic = 0;
startTimer()
      function startTimer()
          ticCount = ticCount+1;
          if ticCount>10
              fprintf('We''ve already reached the end!!!!\n')
              return;
          end
          lastTic = tic;
          fprintf('Starting the timer for time number %d\n',ticCount)
          justWait(5)
      end
      function kp(~,evnt)
          fprintf('User pressed %s\n',evnt.Character)
          if evnt.Character == 'q'
              fprintf('It took the user %g seconds...\n', toc(lastTic))
              startTimer()
          end
      end
      function justWait(len)
          oldTicCount = ticCount;
          fprintf('About to wait for %g seconds...\n',len)
          pause(len)
          if ticCount==oldTicCount
              fprintf('Nothing happened for %g seconds...\n',len)
              startTimer()
          end
      end
  end

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When you define the timer's callback as a string, it is evaluatred in the base workspace. Therefore you cannot observe changes in the variable |stat|inside the show function. Better use a flag which is "attached" to the timer, e.g. its UserData:

t = timer('TimerFcn', @myTimerCB, 'StartDelay', sec, 'UserData', 0);
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MATLAB: Use keyboard input to assign value to a variable

I'm guessing that you will have some sort of GUI or even just a figure that has the displayed image. And so long as your GUI or figure has focus, then you want it to respond to the key presses and act accordingly.

You can do this by simply adding a Key Press callback to a figure. When the user presses a key, the callback will fire and you can handle the event based on the key.

A very simple example that will change the image upon pressing the left and right arrows is

 function catchKeyPress
    h = figure; 
    set(h,'KeyPressFcn',@KeyPressCb) ;
    I = imread('someImageA.jpg');
    imshow(I);
    function KeyPressCb(~,evnt)
        fprintf('key pressed: %s\n',evnt.Key);
        if strcmpi(evnt.Key,'leftarrow')
            I = imread('someImageB.jpg');
            imshow(I);
        elseif strcmpi(evnt.Key,'rightarrow')
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        end  
    end
 end

The above will create a figure and assign a callback for the KeyPressFcn event. The body of the callback fires for every key pressed and, in this case, handles the left and right arrow keys.

Try it and see what happens!

Best Answer

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