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hangyu authored
1. Set cacheExtent for sliverAppBar so it's not dropped from the semantics tree. 2. Update its toolbarOpacity in a11y mode to 1.0. When scrolling in a11y mode and the focus is back to the sliverAppBar, the content should be visible. fixes: https://github.com/flutter/flutter/issues/143437 ## Pre-launch Checklist - [ ] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [ ] I read the [Tree Hygiene] wiki page, which explains my responsibilities. - [ ] I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement]. - [ ] I signed the [CLA]. - [ ] I listed at least one issue that this PR fixes in the description above. - [ ] I updated/added relevant documentation (doc comments with `///`). - [ ] I added new tests to check the change I am making, or this PR is [test-exempt]. - [ ] I followed the [breaking change policy] and added [Data Driven Fixes] where supported. - [ ] All existing and new tests are passing. If you need help, consider asking for advice on the #hackers-new channel on [Discord]. <!-- Links --> [Contributor Guide]: https://github.com/flutter/flutter/wiki/Tree-hygiene#overview [Tree Hygiene]: https://github.com/flutter/flutter/wiki/Tree-hygiene [test-exempt]: https://github.com/flutter/flutter/wiki/Tree-hygiene#tests [Flutter Style Guide]: https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo [Features we expect every widget to implement]: https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo#features-we-expect-every-widget-to-implement [CLA]: https://cla.developers.google.com/ [flutter/tests]: https://github.com/flutter/tests [breaking change policy]: https://github.com/flutter/flutter/wiki/Tree-hygiene#handling-breaking-changes [Discord]: https://github.com/flutter/flutter/wiki/Chat [Data Driven Fixes]: https://github.com/flutter/flutter/wiki/Data-driven-Fixes
