Freezed window

luca.paolini

Hi all,
is my first time in a form so, if I made mistakes, sorry...
I wrote a simply program that get images from udp channel and show them in my MainWindow, also I show some counter.
The program work fine and fast but MainWindows is not sizable, is not movable, clicking button nothing happens.

Now I try to explain my problem:
there are 2 classes, one for mainwindows and one for udp channel; these classes are connected by two signals and two slots

@int main(int argc, char *argv[])
{
QApplication a(argc, argv);
Camera *camera = new Camera();
camera->show();

udpCameraManager *cameraManager = new udpCameraManager();

QObject::connect(cameraManager,SIGNAL(ImageReadySignal(QByteArray*)),camera,SLOT(DoDrawImage(QByteArray*)));

QObject::connect(camera,SIGNAL(Ready(void)),cameraManager,SLOT(GetImage(void)));

camera->cameraManager = cameraManager;
return a.exec&#40;&#41;;

}
@

Clicking a button the first GetImage happen and the download starts. GetImage is:

@ void GetImage()
{
QByteArray Data;
Data.append("Hello from UDP");

  // Sends the datagram datagram
  // to the host address and at port.
  // qint64 QUdpSocket::writeDatagram(const QByteArray & datagram,
  //                      const QHostAddress & host, quint16 port)
  QHostAddress RemoteHost;
  RemoteHost.setAddress("10.2.128.2");

  connect(socket, SIGNAL(readyRead()), this, SLOT(slotReadData()));

  socket->writeDatagram(Data, RemoteHost, 11000);

}
@

then slotReadData emit ImageReadySignal that is connected to DoDrawImage; DoDrawImage create image, call QWidget::repaint() and emit Ready signal; Ready signal is connected to GetImage.
My paintEvent is:

@void Camera::paintEvent(QPaintEvent *event)
{
if(!DoIt)
return;
QPainter painter(this);

if (!image.isNull())
{
    painter.drawImage(10,10,image);
    ImgCounter++;
    double difference = (time.elapsed() / 1000);

    QRect rect = QRect(670, 140, 180, 20);
    painter.drawText(rect,Qt::AlignLeft,"difference: " + QString::number(difference,'f',2));

    rect = QRect(670, 170, 180, 20);
    if(difference > 0)
    {
        double fps = (double)ImgCounter/(double)difference;
        painter.drawText(rect,Qt::AlignLeft,"fps: " + QString::number(fps,'f',2));
    }
    rect = QRect(670, 200, 180, 20);
    painter.drawText(rect,Qt::AlignLeft,"Images: " + QString::number(ImgCounter));
}

}
@

butterface

For me that sounds like an infinite loop of your signal and slot connections. Is that possible?

luca.paolini

Yes it is, I need to download and show continuosly, but I dont know how to solve the freeze, I'm new on Qt programming.
Thanks

butterface

Your slots should do as little work as possible because staying in a slot blocks the event queue. You can use QThread for example to download the image. When it is finished call a slot to display it. If it fits your needs you can also use QTimer to update you UI every x milliseconds.
There are a few possibilities to periodically update your UI but a major rule is to never block the event queue.

luca.paolini

OK,
I'll try it and I'll answer as soon as possible.
Thanks alot for your suggestions.