trouble with height-for-width

django.Reinhard

Hi,

I'm playing with flowlayout-example and added some dialog-like widgets of constant size.
This is a screenshot of all children in a big-enuf container:

... but I don't have that plenty space in my app, so real app-window looks like this:

Layout works as expected, but elements outside of visible container can't be accessed.

So I added a QScrollArea, which leads to this picture:

Now layout does not calculate any other possible width, as the smallest width could be made high enuf for all children.

I don't want to limit height of scrollarea - number of children and (constant) size is variable. So I'm looking for a way to change layout so that first the width is occupied, before wrapping happens.

I guess to achieve that, I have to overload some internal Qt classes. If anybody has done something similar, a helping hand is appreciated!

SGaist

Hi,

Are you applying the layout on the QScrollArea itself or on a widget that you set on the QScrollArea ?

django.Reinhard

Hi,

I was puzzled by your question. I was about to write "of course I assigned the layout to the widget that was included in the scrollarea ...", but then I thought: Hey, why not ...
... and tried it out: Unfortunately, after adding the layout, the ScrollArea was no longer a ScrollArea. At least there were no scrollbars and the ContentArea was also fixed.

Now I don't know what to do. Should I assign the layout to the ScrollArea and research why there are no scrollbars anymore, or was the first way more correct?

In between I thought maybe I could use the resize event to make the layout recalculate from the top, but after a resize event so much goes off internally that I have no plan what I need from it, or how to get my layout to act only on my request.

JonB

@django-Reinhard
@SGaist was just verifying that you did indeed assign layout to widget, not to scroll area. This is correct way.

django.Reinhard

Hi,

just to close this:

I compiled a Qt with debug info and debugged the layout process. Then I thought, I should extend QLayout::totalSizeHint() - but that function is not virtual. So patching Qt would become expensive :(

So I thought, may be QScrollArea has a property for preferred extend direction - which is not the case.
But on that research I discovered QScrollArea::setWidgetResizable() ...

Oh happy day! That did the trick :)

I have nothing to extend or patch, just use this property.
What a revelation :D

Finally my code looks something like this:

Window::Window()
 : client(new QWidget(this)) {
  FlowLayout*  fl = new FlowLayout;
  QScrollArea* sa = new QScrollArea;

  setLayout(new QVBoxLayout);
  layout()->setMargin(0);
  client->setLayout(fl);  
  fl->setMargin(0);

  fl->addWidget(...);
  fl->addWidget(...);
  ...

  sa->setWidget(client);
  sa->setWidgetResizable(true);
  layout()->addWidget(sa);
  }

... and the result looks like:

Yeah!