Tag: dart

A version-pinned guide to moving a legacy Flutter 2.x app to a current Flutter 3.x release, with the sound null safety migration as the hard gate: why you need a two-hop path through Dart 2.19, what dart migrate does, and what breaks along the way.

A step-by-step migration from the provider package to Riverpod 3.x in a real Flutter app: ChangeNotifierProvider to Notifier, MultiProvider to ProviderScope, context.watch to ref.watch, ProxyProvider to ref.watch composition, plus the equality and lifecycle gotchas that bite. Tested on Flutter 3.27.1, Dart 3.11, provider 6.1.5, flutter_riverpod 3.3.1.

Use FutureBuilder or StreamBuilder for a self-contained, throwaway async widget. Reach for Riverpod AsyncValue once the result is shared, cached, or mutated. Here is the decision, the gotchas, and runnable code for both. Tested on Flutter 3.44 and flutter_riverpod 3.3.1.

This crash means a WidgetRef was used after its widget left the tree, usually in an async callback. Read what you need before the await, then guard with a mounted check.

This crash means you called context.of() after the widget left the tree, usually in an async callback or dispose(). Capture the value before the await, or in didChangeDependencies().

FutureBuilder re-runs your async work every time the parent rebuilds because you created the Future inside build. Hoist it into State.initState (or memoize it), and FutureBuilder will reuse the same Future. Here is the why, the repro, and every variant that bites.

Dart 3.12 adds an experimental primary constructors syntax that declares fields and a constructor in the class header, collapsing the classic three-line data class to one.

Pick Riverpod for most new Flutter apps in 2026. Choose Bloc for large teams that want an enforced event-driven structure, and keep Provider only for legacy code.

RenderBox was not laid out is almost always a secondary error. Find the first layout assertion above it, usually a scrollable given unbounded constraints, and fix that.

This crash means code touched a controller after dispose() ran. Guard async callbacks with a mounted check, and never dispose a controller you do not own.