QTreeView - show expand indicator/arrow for parents without children (lazy loading)

[esoteric]

I am trying to make a QTreeView use lazy loading. canFetchMore() and fetchMore() are not working as expected.

Expected: QTreeView items with children that aren't loaded yet but report canFetchMore() -> true should show the expand arrows even when rowCount() -> 0. When the arrow is clicked fetchMore() is called, rowCount() is updated and the items are shown

Actual: No arrows for items without children, even if they can be lazily loaded.

What is the best way to do this? I thought about showing them with a QStyledItemDelegate, but I can't find the right function(s) to call.

[JonB]

@esoteric
Just one thought: what do you have QAbstractItemModel::hasChildren() return when rowCount() == 0? I think it needs to return true for the expander to be shown?

[esoteric]

Hi Jon - I wasn't overriding hasChildren() before, looking at QAbstractItemModel the default implementation is

    return (rowCount(parent) > 0) && (columnCount(parent) > 0);

However I overrode hasChildren() to return true for all folders, but it doesn't make a difference.

[esoteric]

I have a QSortFilterProxyModel, and it looks like hasChildren() doesn't work by itself. It also needs canFetchMore().

[JonB]

@esoteric
I didn't say hasChildren() works on its own. My reading suggests you need both that and canFetchMore() to return true (when rowCount() == 0) for the QTreeView to show expanders. But are you saying that even with both is still does not work?

[esoteric]

@JonB Sorry, yes, it does work with both. Thanks for your help.