Description

Add the collapsedHeight param to the SliverAppBar, allowing for users to set the minimum height when it is collapsed.

SliverAppBar with collapsedHeight set:

Floating SliverAppBar with collapsedHeight set:

SliverAppBar that is floating, pinned, has a bottom widget, with collapsedHeight and expandedHeight set:

Related Issues

Closes #21298

Tests

I added the following tests:

• SliverAppBar expandedHeight, collapsedHeight
• pinned && floating && bottom && extraToolbarHeight != 0.0 ==> 1.0 opacity
• !pinned && !floating && !bottom && extraToolbarHeight != 0.0 ==> fade opacity

Checklist

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• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I signed the CLA.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I updated/added relevant documentation (doc comments with ///).
• All existing and new tests are passing.
• The analyzer (flutter analyze --flutter-repo) does not report any problems on my PR.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Did any tests fail when you ran them? Please read Handling breaking changes.

• No, no existing tests failed, so this is not a breaking change.
• Yes, this is a breaking change. If not, delete the remainder of this section.
  • I wrote a design doc: https://flutter.dev/go/template Replace this with a link to your design doc's short link
  • I got input from the developer relations team, specifically from: Replace with the names of who gave advice
  • I wrote a migration guide: https://flutter.dev/go/breaking-changes-template Replace this with a link to a pull request that adds the migration guide to https://flutter.dev/docs/release/breaking-changes