Explain why initState() is too early to depend on an inherited widget - #192727

Roll Flutter from 4249ccbc18a3 to 426be968b5eb (44 revisions)

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2026-10-14 [email protected] Allow color delta tolerance in in-memory fuzzy image comparator (flutter/flutter#193937)
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2026-10-13 [email protected] Explain why initState() is too early to depend on an inherited widget (flutter/flutter#192727)
2026-10-13 [email protected] Refactor TestPlatformDispatcher (flutter/flutter#192747)
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If this roll has caused a breakage, revert this CL and set the roller
...

…flutter#192727)

When `dependOnInheritedWidgetOfExactType()` is called before
`initState()` has completed, the error explains the rule like this:

> When an inherited widget changes, for example if the value of
Theme.of() changes, its dependent widgets are rebuilt. If the dependent
widget's reference to the inherited widget is in a constructor or an
initState() method, then the rebuilt dependent widget will not reflect
the changes in the inherited widget.

That last sentence is easy to read as saying the rebuild itself does not
see the change, which is what the issue reports as confusing. The
rebuild does see it: a widget that depends on an inherited widget is
rebuilt when that inherited widget changes, and a `build()` method that
reads it gets the new value. What is never updated is whatever
`initState()` read, because the framework calls `initState()` only once
for each `State` object and does not call it again for those rebuilds.

This replaces that sentence with the actual reason, and adds the same
reason to `State.initState`'s documentation, which told readers not to
call `dependOnInheritedWidgetOfExactType()` there but not why. The
`ErrorHint` that points at `build()` and `didChangeDependencies()` is
unchanged.

After:

> When an inherited widget changes, for example if the value of
Theme.of() changes, its dependent widgets are rebuilt. The framework
calls initState() only once for each State object and does not call it
again for those rebuilds, so a value that initState() reads from an
inherited widget is never updated when that inherited widget changes.

The existing test for this error (`initState() dependency on Inherited
asserts`) only checks that something was thrown, so the message itself
was untested; the new test covers it. `ExpectFail` now forwards the
caught error so a test can inspect it.

The issue also suggests adding a `_StateLifecycle` value between
`created` and `initialized`, set just before `initState()` is called. I
left that out. A `State` only gets its context after it is constructed
(`state._element` is assigned in the `StatefulElement` constructor after
`createState()` returns), so the only `State` code that runs with a
context before `initState()` completes is `initState()` itself, and a
new value would have no constructor case to separate. That is also why
the new message no longer mentions constructors; the general advice
about constructors stays in the
`BuildContext.dependOnInheritedWidgetOfExactType` docs.

Fixes flutter#105705

## Pre-launch Checklist

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we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant in-code documentation (doc comments with
`///`).
- [x] If this PR introduces a new feature or capability, I created and
linked a website documentation issue or PR in [flutter/website] (or
verified none is needed).
- [x] I added new tests to check the change I am making, or this PR is
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- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

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