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Tag: dart

86 posts · Page 4 of 9

2026-07-18 errors flutter dart

Fix: ScaffoldMessenger.of() was called with a context that does not contain a Scaffold (Flutter)

This error means the BuildContext you passed is above the Scaffold or ScaffoldMessenger, not below it. Wrap the caller in a Builder, extract it into its own widget, or use a GlobalKey.

2026-07-18 errors dart flutter

Fix: type 'Null' is not a subtype of type 'X' in Dart

This runtime error means a null reached a cast expecting a non-nullable type, almost always from JSON. Make the field nullable, or supply a default before the cast runs.

2026-07-14 flutter dart animation

How to add a Hero animation between two screens in Flutter

Wrap the same widget on both routes in a Hero with an identical tag and Flutter animates its position and size across the navigation. Full guide: images, flightShuttleBuilder, createRectTween, RectTween arcs, gesture transitions, and the tag collisions that break it. Tested on Flutter 3.44, Dart 3.12.

2026-07-13 flutter dart async

How to cancel a StreamSubscription in dispose to avoid a setState-after-dispose crash in Flutter

A stream keeps emitting after the user leaves the screen, its onData calls setState on a disposed State, and Flutter throws. Store the subscription, cancel it in dispose before super.dispose, and the callback can never fire on a dead widget. The full pattern for Flutter 3.44.

2026-07-13 flutter dart async

How to guard setState with the mounted check after an async gap in Flutter

After an await, the widget may already be disposed, and calling setState throws. Guard the resume with if (!mounted) return; and, better, cancel the work that triggers it. The full pattern for Flutter 3.44.

2026-07-09 migration flutter dart

Migrate from Riverpod 2.x to Riverpod 3.0 in Flutter

A step-by-step upgrade from flutter_riverpod 2.x to 3.x: bump the packages, move StateProvider and friends to the legacy import, drop the AutoDispose and Family ref types, handle ProviderException wrapping and automatic retry, and fix the == notification filtering that silently drops StreamProvider events. Tested on Flutter 3.44, Dart 3.x, flutter_riverpod 3.3.2.

2026-07-07 flutter dart

Flutter 3.44: Read the Physical Screen Corner Radius from MediaQuery

Flutter 3.44 exposes the device's rounded display corners through MediaQuery.displayCornerRadiiOf. Stop guessing a magic radius and clip your UI to the exact hardware curve on Android API 31+.

2026-07-07 flutter dart go-router

go_router vs auto_route vs Navigator 2.0 in Flutter

go_router and auto_route both sit on top of Navigator 2.0, so the real choice is declarative URL routing vs code-generated typed routes vs hand-rolling the Router API. A decision matrix with config for each, and when raw Navigator still wins.

2026-07-07 comparison flutter dart

shrinkWrap vs Expanded vs slivers for long lists in Flutter: which should you pick?

For a long list, never use shrinkWrap. Use Expanded when the list is the only scrollable, and slivers (CustomScrollView) when it shares a scroll with other sections. Here is why, with a build-count benchmark.

2026-07-06 errors flutter dart

Fix: Riverpod 3.0 throws ProviderException instead of the original error

Riverpod 3.0 wraps errors thrown while reading a provider in a ProviderException. Catch that type and read e.exception to get your original error back, or use AsyncValue.error which is unwrapped.