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Snapshot grid structure info instead of modifying it in place #12646
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The failed UI tests are on UWP, and both of them pass locally. I'm certain the test failures are unrelated to these changes. |
hartez
added
i/high
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I had the exact same problem. For our project this PR is actually what can fix the problems we are getting in 4.8 with this. We backported this to 4.8 in a custom build but it seems to be generating other problems. I think this PR should be a major priority for 5.0. |
PureWeen
approved these changes
Nov 5, 2020
rmarinho
approved these changes
Nov 11, 2020
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Nice <3 gz @hartez |
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Description of Change
Issue #6247, issue #10470, and https://forums.xamarin.com/discussion/88367/nullreferenceexception-on-grid-calculateautocells-only-xf-ios describe NullReferenceExceptions accessing the
_rowsand_columnsmembers during Grid layouts. These members are lists of RowDefinition and ColumnDefinition information used during the measurement and layout of the Grid. The information in these lists is not for caching purposes; lists are reset during every measurement and layout operation, and also when computing constraints for the Grid.Because the lists are nullable, certain layout and update conditions (which are very difficult to consistently reproduce) can result in the lists being null while a measurement operation is taking place, crashing the application.
In https://github.com/xamarin/Duplo/pull/3675, a similar issue during LayoutChildren was addressed by snapshotting the lists before handling layout, in case InvalidateMeasure was called during the layout process. These changes formalize that snapshotting by creating a separate class to handle creating the snapshot and using it in LayoutChildren, OnSizeRequest, and ComputeConstraintForView. The nullable lists of row/column definitions have been removed entirely, so a NullReferenceException is no longer an issue.
Issues Resolved
API Changes
None
Platforms Affected
Behavioral/Visual Changes
None
Before/After Screenshots
Not applicable
Testing Procedure
No new tests
PR Checklist