Trigger recompute of QListView item display

Chris Hennes

I've got a QListView that shows my items in two different modes, expanded and condensed. That's implemented using a delegate that overrides paint() and sizeHint(). paint() loads my model data into a custom widget and renders it into the painter, and sizeHint() returns that widget's sizeHint(). This works great for each individual mode, but when I cycle between them, the items that are currently onscreen are not updated to the new display, and the height of the rows stays at the height of the Expanded view's size hint (92px), even when sizeHint() starts returning the compact view's height(38px). What step am I missing to trigger the redraw of the current window contents, and to get the view to update to use the new sizeHint() for its row height calculation?

Christian Ehrlicher

You can try to emit a dataChanged() signal with the SizeHint role.

Chris Hennes

Good thought, thanks. Closer now, but still not quite there. The widgets all update when I mouse over the view now (but not before that), but their height stays the same as it was. For the record, here's what my (still not working) update function is doing right now:

        self.ui.listPackages.updateGeometries()
        self.item_model.layoutChanged.emit()
        startIndex = self.item_model.index(0,0)
        endIndex = self.item_model.index(self.item_model.rowCount()-1,0)
        self.item_model.dataChanged.emit(startIndex, endIndex, Qt.SizeHintRole)
        for i in range(0,self.item_model.rowCount()):
            index = self.item_model.index(row,0)
            self.item_delegate.sizeHintChanged.emit(index)

I'm basically just throwing everything I can think of at it now, obviously once I find the real solution most of this will go away.

Christian Ehrlicher

Not a python expert but dataChanged() needs a list/vector for the roles. If it would be c++ I would have called for a minimal example so I can check it out (there is a similar question around: https://forum.qt.io/topic/132284/ ).
What exact Qt version do you use?

JonB

@Christian-Ehrlicher said in Trigger recompute of QListView item display:

Not a python expert but dataChanged() needs a list/vector for the roles.

If it makes any difference @Chris-Hennes should try

self.item_model.dataChanged.emit(startIndex, endIndex, [Qt.SizeHintRole])

Chris Hennes

I tried with the role set to various things (as a list), but my basic impression is that nothing in Qt internally uses the role argument to dataChanged(), and it didn't have any effect here. I can create a short C++ example after the holiday here, if no other solution arises. I'm doing this development on 5.15, but any chosen solution has to work on 5.12 as well.

Christian Ehrlicher

Is it the same problem (in python) like here https://forum.qt.io/topic/132284/ ?

Chris Hennes

It's not the same problem, though it's possible they have related solutions: my rows aren't editable, so I don't create an editor widget at all, this is the main display that's not working quite right. I suspect in my case it's two independent problems. The first is that I need to trigger the QListView to redraw itself (which should trigger the paint() function in my delegate for the on-screen rows), and the second is that I need the QListView to actually use the sizeHint() that it's getting from that delegate.

Chris Hennes

OK, the answer turns out to be that I had an error elsewhere in my code that was masking the real problem. To get the update done all I actually need is

self.item_model.layoutChanged.emit()

Thanks again for the assistance.