Qt QWidget :: minimumSizeHint延迟（＃2）

Question

When i hide a widget in my application, the minimumSizeHint isn't updated immediatly.

I tried the QLayout::activate() solution suggested at this post , but it doesn't work for me because QLayout::activate() returns false .

I try to do it at MainWindow class like this:

ui.groupBox->setVisible(!ui.groupBox->isVisible());

qDebug() << this->layout()->activate();

qDebug() << this->minimumSizeHint();

this->resize(this->minimumSizeHint());

Any ideas why it's not working?

My current workaround is:

QTimer::singleShot(10, this, SLOT(on_resizeMin()));

but i noticed 10ms may not be enough on a slow system. Nasty workaround.

Answer 1

The size hints are meant to be used at appropriate moments by the layout system. You're not supposed to be using them elsewhere - that's why they appear to "not work".

You appear to want to constrain the size of the main widget (the window) to one of the size hints. You'll need to set an appropriate sizeConstraint on that widget's layout. There are two approaches:

1. Use the QLayout::SetFixedSize constraint. Reimplement the layout's sizeHint to return minimumSize , such that the QLayout::SetFixedSize will set the window's size to the minimum size hint, not the default size hint.

2. Patch Qt to implement QLayout::SetMinAndMaxToMinSize , meaning "The main widget's minimum and maximum size are set to minimumSize() "

   The patch is small :)