Make VirtualizingStackPanel better handle container size changes #16168
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If any container U size has changed since the last layout pass then `StartU` must be considered unstable as the average container height will have changed.
If the focused element has been moved outside the visible viewport due to a realized container size change, then we need to ensure it's positioned correctly.
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You can test this PR using the following package version. |
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Marking this as a draft because I've discovered that it's not working quite as intended. |
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Marked this PR as ready for review again. It isn't perfect but it's better than before and a better fix will be more involved. The problems are twofold:
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Hello, I still have issue with the _focusedElement if you zoom out, select one element (to set the _focusedElement) then if you scroll to make it disappear of the viewbox, then zoom in/scroll , you'll have a ghost item representing the _focusedElement. |
And revert the expected results for another test to the way they were at the beginning of this PR.
Use the desired size of _measured_ containers instead of the bounds: a layout pass may not had completed on the containers yet, so the bounds may not be up-to-date. Was easier to move the estimation methods out of `RealizedStackElements` and into `VirtualizingStackPanel` itself in order to do this, and arguably makes more sense.
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Thanks for testing @Whiletru3 - I've updated the PR to address some of the concerns I had with the original naïve approach and hopefully this should have fixed the issue you were seeing. |
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You can test this PR using the following package version. |
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Hello @grokys , Using your last changes, I can't reproduce the issue :) Now, I just have to tackle the issue of keeping the offset when zoom in or out. |
maxkatz6
added
backport-candidate-11.0.x
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@Whiletru3 this PR will go into 11.1.1. But it might be backported to the 11.0.x, I will lable it for the consideration. |
) * Add a failing test for #15712. * Validate StartU at the start of a measure pass. If any container U size has changed since the last layout pass then `StartU` must be considered unstable as the average container height will have changed. * Correctly position focused element. If the focused element has been moved outside the visible viewport due to a realized container size change, then we need to ensure it's positioned correctly. * We can skip check if StartU is already unstable. * Don't invalidate virt. panels more than necessary. * Add another virt panel test. And revert the expected results for another test to the way they were at the beginning of this PR. * Tweak container size estimation. Use the desired size of _measured_ containers instead of the bounds: a layout pass may not had completed on the containers yet, so the bounds may not be up-to-date. Was easier to move the estimation methods out of `RealizedStackElements` and into `VirtualizingStackPanel` itself in order to do this, and arguably makes more sense.
) * Add a failing test for #15712. * Validate StartU at the start of a measure pass. If any container U size has changed since the last layout pass then `StartU` must be considered unstable as the average container height will have changed. * Correctly position focused element. If the focused element has been moved outside the visible viewport due to a realized container size change, then we need to ensure it's positioned correctly. * We can skip check if StartU is already unstable. * Don't invalidate virt. panels more than necessary. * Add another virt panel test. And revert the expected results for another test to the way they were at the beginning of this PR. * Tweak container size estimation. Use the desired size of _measured_ containers instead of the bounds: a layout pass may not had completed on the containers yet, so the bounds may not be up-to-date. Was easier to move the estimation methods out of `RealizedStackElements` and into `VirtualizingStackPanel` itself in order to do this, and arguably makes more sense.
grokys
removed
the
backport-candidate-11.1.x
What does the pull request do?
As described in #15712, if a container changes size after layout then glitches occur when scrolling.
To fix this:
StartUis no longer valid because the average element size will have changed, so mark is as unstableRealizedStackElementsand intoVirtualizingStackPanelitself in order to do this, and arguably makes more senseFixed issues
Fixes #15712