[camera] Fix CameraController may update after dispose and crash with "used after being disposed. (fixes #184959)

[Istiak-Ahmed78]

Fixes flutter/flutter#184959

Description

Fixed a critical race condition bug in the camera package where async callbacks in CameraController._initializeWithDescription() could execute after dispose() is called, causing a crash: "A CameraController was used after being disposed. Once you have called dispose() on a CameraController, it can no longer be used."

Root Cause

In _initializeWithDescription(), three async fire-and-forget callbacks had no dispose guards:

// Line 341-346: _deviceOrientationSubscription listener
_deviceOrientationSubscription ??= CameraPlatform.instance
    .onDeviceOrientationChanged()
    .listen((DeviceOrientationChangedEvent event) {
      value = value.copyWith(deviceOrientation: event.orientation);  // NO GUARD!
    });

// Line 363-365: onCameraError callback
unawaited(
  CameraPlatform.instance.onCameraError(_cameraId).first.then((
    CameraErrorEvent event,
  ) {
    value = value.copyWith(errorDescription: event.description);  // NO GUARD!
  }),
);

// Line 358-371: Main value assignment (THE CRASH POINT)
value = value.copyWith(
  isInitialized: true,
  description: description,
  previewSize: await initializeCompleter.future.then(...),
  exposureMode: await initializeCompleter.future.then(...),
  ...
);  // NO GUARD! This is line 364 in the crash stack trace

The Issue: When dispose() is called while these callbacks are still pending:

1. dispose() sets _isDisposed = true
2. Async callbacks later resolve
3. They call value = ... which calls notifyListeners()
4. notifyListeners() throws because the controller is disposed

Solution

Added if (!_isDisposed) guards before every value = ... assignment in async contexts within _initializeWithDescription().

Pre-launch Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I read the [Tree Hygiene] 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 added/updated tests for this change.
• I used self-descriptive commit messages.

[navaronbracke]

Could these use early returns? That would reduce the indent changes in code.

Just a personal preference though.

[Istiak-Ahmed78]

Thanks for the suggestion! Early returns would definitely improve the code.

However, this PR is still in draft. @mbcorona from the Flutter team recently
discovered a deeper issue: ImageReader fails to drain pending frames on dispose,
flooding the queue with 290+ orphaned callbacks.
flutter/flutter#184959 (comment)

My current fix addresses the symptom (guarding state updates). but the root cause is the improper ImageReader cleanup at the native
level. So I'm currently reinvestigating the issue

Once I resolve the frame leakage issue, I'll:

• Apply your early return suggestion
• Update the fix comprehensively
• Mark it ready for review

Thanks again for your suggestion!

[stuartmorgan-g]

Before marking it ready for review, please update the PR to use and follow our actual checklist, rather than an AI-hallucinated checklist.