Currently if you want to create a MaterialStateProperty that always returns the same value regardless of the current states, you could use the .all static method:

final color = MaterialStateColor.all<Color>(Colors.blue);

However this can be a const value which makes it harder to use with const ButtonStyles and other structures that could be const otherwise.

This PR adds a new MaterialStatePropertyAll class that allows you to convert the above code to:

const color = MaterialStateColorAll<Color>(Colors.blue);

Which can then be used in other const structures.

We may deprecate MaterialStateProperty.all in the future, but didn't want to do this without a dart fix for it. As it turns out, this isn't a case that can be currently handled by dart fix. When it is, we will probably deprecate it.

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].
• All existing and new tests are passing.