Setting QMainWindow at the center of screen

Question

My QMainWindow contains a QGraphicsView, which should've minimum width and height. So, I've used the following code in the QMainWindow connstructor:

ui.graphicsView->setMinimumHeight(VIEWWIDTH);
ui.graphicsView->setMinimumWidth(VIEWWIDTH);

Then I used following code to set QMainWindow at the center of the screen:

QRect available_geom = QDesktopWidget().availableGeometry();
QRect current_geom = frameGeometry();
setGeometry(available_geom.width() / 2 - current_geom.width() / 2,
   available_geom.height() / 2 - current_geom.height() / 2,
   current_geom.width(),
   current_geom.height());

But it is not set at the center of the screen. If I omit setMinimumHeight() and setMinimumWidth() from QGraphicsView, then the main window is set at the center of the screen. How to overcome this problem? I'm using Qt 4.5.2.

Thanks.

Answer 1

The problem you are encountering is that Qt will delay many calculations as long as it can. When you set the minimum width and height of your graphics view, it sets a flag somewhere that the window the graphics view is in needs re-layed out. However, it won't do that until it has to... a few milliseconds before it is actually shown on screen. So, when you call rect() on your main window, you are getting the old rectangle, and not the new one.

My best recommendation is to extend the size change event in your main window, and adjust the positioning in that event. You may also have to flag when the window has actually been shown, so that you don't reposition the window if the user resizes it after it has been shown.

Alternately, you could try repositioning the window by extending the show event function and doing it there. It would probably happen before the user actually sees the window, but might flicker on occasion.