84f61dd2d2
When the layout changes, we mark all rows as changed but do not track where the individual rows get moved. The only reason why one would want to track the moves is to persist the current item selection across a layout change. But even the previous code did not achieve that. I'll create a follow up patch to this one that also implements this behavior as seen in Qt Widget item views. Note that removing this code brings a tremendous performance win on larger models. The repeated calls to _q_itemsMoved triggered O(n^2) behavior in the number of top items in the model. Even with "only" tens of thousands of items in the model, a layout change became very costly and took seconds on a beefy modern desktop machine. Calling _q_itemsMoved in a loop is bad because it: - leads to O(N^2) behavior within QQmlChangeSet when merging the small moves into the item view's current change set - potentially triggers tons of binding/property updates when the cached model indices are updated in _q_itemsMoved Removing this slow path, I did not yet find a behavior change to the previous code. Instead, it just does it all much faster. Change-Id: I67fa99a1c5d8e05d17497d29391da9458bd9bdd0 Task-number: QTBUG-51638 Reviewed-by: Daniel Vrátil <daniel.vratil@kdab.com> Reviewed-by: Robin Burchell <robin.burchell@viroteck.net> |
||
|---|---|---|
| .. | ||
| 3rdparty/masm | ||
| imports | ||
| particles | ||
| plugins | ||
| qml | ||
| qmldebug | ||
| qmldevtools | ||
| qmltest | ||
| quick | ||
| quickwidgets | ||
| src.pro | ||