限制QWidget的大小

Question

Let's say I have an wall where user can have only N windows. I should restrict the user from setting one window over another. He can move, resize them but he cannot overlap them. To ignore the invalid moves I am catching the moveEvents and if the event->pos() is an invalid position I reset the geometry to the event->oldPos() . Well this approach is not working for resizeEvent .
Why I can't use same approach on resize?
How can I solve this problem?

PS Setting maximumSize and minimumSize is not a good idea, it's to consuming because of my implementation.

Answer 1

When a user resized a window or resize is called Qt sets Qt::WA_WState_ConfigPending flag to true and starts internal resize operations. During these operations you receive resizeEvent . If you try to call resize there Qt just checks that the flag is set and ignores new resize until previous one is finished, however it sends resizeEvent again with the same data and you get into an endless recursion.

You can use this trick to overcome the check:

void widget::resizeEvent(QResizeEvent* e)
{
    if (e->size().width() > 800)
    {
        setAttribute(Qt::WA_WState_ConfigPending, false);
        resize(e->oldSize());
    }
}

However, you still get blinking of the window, because it's already resized when you get resizeEvent . Actually OS resizes a window and then sends WM_SIZE message to a window to handle the change, that's why you have to deal with the result of the resize operation.