Riverpod ref.read() in dispose() Error

Problem

When a ConsumerStatefulWidget needs to call a service method in dispose() (e.g., to cancel an operation when the user leaves a screen), using ref.read() throws an error because the widget is already unmounted.

Context / Trigger Conditions

• Error message: Using ref when widget is unmounted is unsafe
• Using ConsumerStatefulWidget with ConsumerState
• Calling ref.read(someProvider) inside dispose()
• Widget navigates away (pop, push replacement, etc.)
• Stack trace shows the error originating from dispose()

Example problematic code:

@override
void dispose() {
  ref.read(authServiceProvider).cancelOperation();  // ERROR!
  super.dispose();
}

Solution

Step 1: Add a late final field for the service

class _MyScreenState extends ConsumerState<MyScreen> {
  late final MyService _myService;  // Cache here

Step 2: Initialize in initState

@override
void initState() {
  super.initState();
  _myService = ref.read(myServiceProvider);  // Safe here
}

Step 3: Use cached reference in dispose

@override
void dispose() {
  _myService.cancelOperation();  // Use cached reference
  super.dispose();
}

Verification

1. Navigate to the screen
2. Navigate away (back button, push replacement, etc.)
3. No "Using ref when widget is unmounted" error in console
4. The cleanup action (cancel, close, etc.) still executes

Example

Before (causes error):

class _NostrConnectScreenState extends ConsumerState<NostrConnectScreen> {
  @override
  void dispose() {
    // ERROR: ref is not safe to use here
    ref.read(authServiceProvider).cancelNostrConnect();
    super.dispose();
  }
}

After (works correctly):

class _NostrConnectScreenState extends ConsumerState<NostrConnectScreen> {
  // Cache AuthService for use in dispose (can't use ref.read in dispose)
  late final AuthService _authService;

  @override
  void initState() {
    super.initState();
    _authService = ref.read(authServiceProvider);
  }

  @override
  void dispose() {
    // Cancel the session if user leaves the screen
    _authService.cancelNostrConnect();
    super.dispose();
  }
}

Notes

• This pattern is necessary because Riverpod's ref is tied to the widget lifecycle
• ref.read() is safe in initState() because the widget is being mounted
• ref.read() is NOT safe in dispose() because the widget is being unmounted
• The late final pattern ensures the service is initialized exactly once
• This applies to any cleanup that requires calling methods on providers
• For simple provider state changes (not method calls), consider using deactivate() instead
• If the service itself might be disposed, add null checks or try-catch as appropriate

Related Skills

• flutter-dispose-timer-test-failure: For timer-related dispose issues
• flutter-deactivate-setstate-during-build: For setState/build cycle issues in deactivate

References

• Riverpod ConsumerStatefulWidget
• Flutter State.dispose