How can I avoid the paintEvent after resizing a widget?

[wysota]

Ok, but how does it differ in your case? Qt calls update() upon resize as well...

[jianliang79]

Ok, but how does it differ in your case? Qt calls update() upon resize as well...

yes, It differ in my case at least when I create my widget as a top level widget. look at the following code(from qapplication_win.cpp) :

QResizeEvent e(newSize, oldSize);
QApplication::sendSpontaneousEvent(this, &e);
if (d_func()->paintOnScreen()) {
    QRegion updateRegion(rect());
    if (testAttribute(Qt::WA_StaticContents))
        updateRegion -= QRect(0, 0, oldSize.width(), oldSize.height());
    d_func()->syncBackingStore(updateRegion);
} else {
    d_func()->syncBackingStore();
}

QResizeEvent e(newSize, oldSize);
QApplication::sendSpontaneousEvent(this, &e);
if (d_func()->paintOnScreen()) {
    QRegion updateRegion(rect());
    if (testAttribute(Qt::WA_StaticContents))
        updateRegion -= QRect(0, 0, oldSize.width(), oldSize.height());
    d_func()->syncBackingStore(updateRegion);
} else {
    d_func()->syncBackingStore();
}

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Qt will just send resizeEvent to my widget and I don't see any of the event handler will call update(). In fact it is done in d_func()->syncBackingStore(); this function will sync the backing store of the top level widget, in my case, it will draw the newly exposed area of the widget immediately(in syncBackingStore() Qt will always deem the newly exposed area as dirty even I have called repaint() in my resizeEvent handler). So if I call repaint() in my resizeEvent handler, the newly exposed area will be redrawn twice.

[wysota]

But why do you want to call repaint() or update() in your resizeEvent at all? It is obvious that a paint event will follow it if necessary. Maybe if you could express what is the purpose of all those manipulations we could suggest a cleaner approach?

[jianliang79]

But why do you want to call repaint() or update() in your resizeEvent at all? It is obvious that a paint event will follow it if necessary. Maybe if you could express what is the purpose of all those manipulations we could suggest a cleaner approach?

Sorry, maybe I don't express my question clearly enough, now I will describe it again:
As I have mentioned in my first post: I am writing a widget, this widget must refresh all the area after a vertical resizing but only need to refresh the newly visible part after a horizontal resizing( a ruler widget may have the same behaviour).
1) If I don't set Qt::WA_StaticContents attribute to my widget, Qt will notify me to redraw the entire area of the widget after any kind of resizing. But in the case of horizontal resizing it will waste a lot time to redraw the unchanged part of my widget. I think this is not an effient way.
2) If I set Qt::WA_StaticContents attribute to my widget, Qt will only notify me to redraw the newly exposed part of my widget after resizing, but in the case of vertical resizing this will make me unable to redraw the entire widget.
It seems that I have to manually control which part of my widget need to be redrawn in resize event handler by comparing the old size and new size of my widget. I am interested in that is there an elegent way to let me control that by myself?
Thanks.

[wysota]

It might prove much easier to cache the looks of your widget and simply rerender the already computed part instead of trying to work around architectures.

[jianliang79]

It might prove much easier to cache the looks of your widget and simply rerender the already computed part instead of trying to work around architectures.

Thanks. I will keep that in mind.