App Designer: Button callback function to stop loop reacts only with delay

3 次查看（过去 30 天）

Lima Kilo 2020-9-14

1
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/593593-app-designer-button-callback-function-to-stop-loop-reacts-only-with-delay

评论： Geoff Hayes 2020-9-15

videoplayer_minimal.mlapp

I'm trying to build a small video player in App designer, with a play / stop button and a UIAxes to display the frames. Once play is clicked, a while loop runs that displays the video frames until the bool_play flag turns false. The callback function of the play / stop button should set this flag. Pressing the stop button will stop the playback, but only with a delay that seems to grow the longer the loop has been running.

There is a pause() in the loop, so it should be interruptible and the callback should be able to execute.

These are the relevant functions:

function PlayButtonPushed(app, event)
     if app.bool_play == false % play video
        app.PlayButton.Text = "Stop";
        app.bool_play = true;
        app.play();
     else % stop video
        disp('stop clicked');
        app.bool_play = false;
        app.PlayButton.Text = "Play";
     end
end
function results = play(app)
    tic
    while app.bool_play == true
        playbackSpeed = 10; % fps
        
        if app.currentFrameNum >= size(app.vid,3)
            app.currentFrameNum = 1; % start over
        end
        app.display_image();
        pauseTime = 1/playbackSpeed;
        timeElapsed = toc;
        restTime = pauseTime - timeElapsed;
        disp([pauseTime timeElapsed restTime]);
        if restTime > 0 && app.bool_play == true
            pause(restTime);
        end                
        tic
        app.currentFrameNum = app.currentFrameNum + 1;
        
    end
end
function results = display_image(app)
    
    frameNum = app.currentFrameNum;
    im = app.vid(:,:,frameNum);
    app.imageHandle = imagesc(app.UIAxes, im);
    app.UIAxes.Title.String = sprintf("Frame %i", frameNum);
    app.currentFrameNum = frameNum;
end

What is the reason for this delay and can it be fixed? Or is there maybe a better approach?

The app file is attached.

Thanks!

2 个评论
显示无隐藏无

Mario Malic 2020-9-14

In your function play, put drawnow maybe with limitrate.

Geoff Hayes 2020-9-15

Lukas - or perhaps use a timer that fires every 1/10 of a second (1/playbackSpeed) to display the frame. You then should be able to stop the timer when the stop button is pressed.

请先登录，再进行评论。

请先登录，再回答此问题。