Fix: Null check operator used on a null value in Flutter
The ! operator hit a null at runtime. Replace it with ?. and ?? for a safe default, or guard with an explicit null check, instead of asserting a value that was not there.
Tag: dart
108 posts · Page 8 of 11
How to set up nested routes and deep links with go_router in Flutter
Build a persistent shell with nested routes using ShellRoute and StatefulShellRoute, then wire up path-based deep links that rebuild the full page stack. Full config for Android and iOS, plus the gotchas that break the back stack.
How to use BuildContext safely after an await in Flutter
Capture what you need from the context before the await, then guard the resume with if (context.mounted) return. Here is the full pattern, the lint that enforces it, and the edge cases it misses.
Migrate a Flutter 2 app to Flutter 3.x: the null safety checklist
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.
Migrate from provider to Riverpod in Flutter (provider 6.1.5 to Riverpod 3.x)
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.
FutureBuilder/StreamBuilder vs Riverpod AsyncValue in Flutter: which should you use?
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.
Fix: Bad state: Cannot use "ref" after the widget was disposed in Flutter Riverpod
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.
Fix: Looking up a deactivated widget's ancestor is unsafe in Flutter
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().
How to Initialize a Future So FutureBuilder Doesn't Recreate It on Every Rebuild in Flutter
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 Ships Primary Constructors Behind an Experiment Flag
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.