Drawing on a qwidget while playing videos

Question

I have a class A that inherits from a class that inherits from QWidget. My class contains a media player and a QVideoWidget. I want my object A to draw a small rectangle for a few milliseconds every time a new video from the play list starts playing, on the part of the widget that isn't the video widget. So, I've connected my slot

connect(player, &QMediaPlayer::currentMediaChanged,this,&videoDisplay::drawRect);

but I can't manage to get the drawRect function right. Tried using QPainter but it gave me errors

QWidget::paintEngine: Should no longer be called
QPainter::begin: Paint device returned engine == 0, type: 1

any advice?

Thanks

Answer 1

Painting in Qt should generally only be performed as the result of an update request.

Rather than try to draw directly you could use a flag or similar to signify a new item has started from the playlist...

bool m_new_video;

Then just use a lambda as the slot and have it set the flag and request an update...

connect(player, &QMediaPlayer::currentMediaChanged,
        [this]()
        {
          m_new_video = true;
          update();
        });

Your videoDisplay::paintEvent implementation can then draw whatever it has to based on the value of m_new_video.