Selecting a region from a QGraphicScene with QRubberBand

Daguerreo

Hello everyone,

I'm trying to select a region of an image in a QGraphicScene with QRubberBand. Following the documentation ( http://doc.qt.io/qt-5/qrubberband.html ) I wrote this:

void MainWindow::mousePressEvent(QMouseEvent *event)
{
	mypoint = event->pos();
	mRubberBand = new QRubberBand(QRubberBand::Rectangle, ui->graphicsView);//new rectangle band

	mRubberBand->setGeometry(QRect(mypoint, QSize()));
	mRubberBand->show();
}

void MainWindow::mouseMoveEvent(QMouseEvent *event)
{
	if(mRubberBand)
	{
		mRubberBand->setGeometry(QRect(mypoint, event->pos()).normalized());//Area Bounding
	}
}

void MainWindow::mouseReleaseEvent(QMouseEvent *event)
{
	if(mRubberBand)
	{
		QRect myRect(mypoint, event->pos());
		mRubberBand->hide();// hide on mouse Release
		QImage copyImage;  //<= this Qimage hold nothing
		mImageInRect = copyImage.copy(myRect);
	}
}

The problem is the code work ONLY if I start selecting out of the GraphicScene and then move, I can't click to the image and start selecting.

Someone could please explain me what's wrong? Thank you

Chris Kawa

You are overriding the mouse*Events in the MainWindow. If you want to detect a mouse press in a QGraphicsView then override mousePressEvent in QGraphicsView (by subclassing it).

Also, you modified the example and created a severe memory drain. You are creating new rubber band object on every mouse press and they will be deleted only when the parent graphics view is destroyed.

Daguerreo

Thank you! I had that doubt about it, but I wasn't sure there wasn't another method more direct than this

About the memory draining, I knew it, I already moved that part to the constructor, I pasted it there to show the all the operation was been done.