Fix: setState() or markNeedsBuild() called during build in Flutter
This error means you mutated state while Flutter was building. Move the setState out of build, or defer it with addPostFrameCallback. Here is why it happens and the right fix.
Tag: dart
95 posts · Page 8 of 10
How to Show Loading and Error States with AsyncValue in Flutter Riverpod
Render loading, data, and error UI from a single AsyncValue in Riverpod 3. Use AsyncNotifier and AsyncValue.guard for mutations, .when() and switch pattern matching for the UI, keep previous data on refresh, and migrate the legacy StateNotifier pattern. Tested on flutter_riverpod 3.x, Flutter 3.44, Dart 3.x.
How to Dispose Controllers in Flutter to Avoid Memory Leaks
AnimationController, TextEditingController, and ScrollController hold resources that Dart's GC cannot reclaim until you dispose them. Here is the correct pattern, the ordering rules, and how to catch leaks before they ship.
How to Handle Network Errors Gracefully in a Flutter App
A request can fail with no connectivity, a timeout, a DNS failure, a 500, or malformed JSON, and each needs a different response. Here is how to catch the right exceptions, classify them, retry safely, and show a UI a user can act on.
The Dart and Flutter MCP server: one command to give Claude Code your running Flutter app
Dart 3.12 ships dart mcp-server, the official MCP bridge into the Dart and Flutter toolchain. Register it once in Claude Code, Cursor, or Codex CLI and your agent gets hot reload, pub.dev search, and live widget introspection without copy-pasting a DTD URI.
Dart records vs Freezed classes: which should you pick in 2026?
Pick Dart 3.12 records for ephemeral, locally-shaped data with no methods, and Freezed 3.x classes for named domain models that need copyWith, sealed unions, JSON serialization, or any behaviour.
Dart 3.12 Drops the Initializer List for Private Fields
Dart 3.12 lets constructors initialize private fields directly with named parameters, killing one of the language's most persistent boilerplate patterns.
Cloud Functions for Firebase Now Speaks Dart (Experimental)
Firebase shipped experimental Dart support for Cloud Functions on May 6, 2026. HTTPS and callable triggers, AOT-compiled cold starts, and the Firebase CLI handles compilation.
Fix: Unhandled Exception: FormatException: Unexpected character when parsing JSON in Dart
The fix in 30 seconds: your response body is not the JSON you think it is. Print the raw bytes, decode with utf8.decode(response.bodyBytes), and never feed an HTML error page or a BOM-prefixed string to jsonDecode.
Fix: Version solving failed in pubspec.yaml
The fix in 30 seconds: read the 'because' chain in the error, find the one constraint that boxes pub in, and either widen it or add a dependency_overrides entry. Do not start with flutter clean.