flutter assertion_error ai_generated true

Assertion failed: MediaQuery.of() called with a context that does not contain a MediaQuery ancestor.

ID: flutter/assertion-error-media-query-before-run

Also available as: JSON · Markdown · 中文
92%Fix Rate
89%Confidence
1Evidence
2023-06-12First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
flutter 3.10 active — — —
flutter 3.22 active — — —
dart 3.0 active — — —

Root Cause

MediaQuery.of(context) is called before the widget is inserted into the widget tree that has a MaterialApp or WidgetsApp ancestor providing MediaQuery, typically during build before runApp() or in a widget that is not a descendant of MaterialApp.

generic

中文

MediaQuery.of(context) 在 widget 被插入到具有 MaterialApp 或 WidgetsApp 祖先（提供 MediaQuery）的 widget 树之前被调用，通常在 build 期间但在 runApp() 之前，或在一个不是 MaterialApp 后代的 widget 中。

Official Documentation

https://api.flutter.dev/flutter/widgets/MediaQuery/of.html

Workarounds

  1. 95% success Ensure MediaQuery.of(context) is only called inside a build method of a widget that is a descendant of MaterialApp or WidgetsApp. If needed in initState, use WidgetsBinding.instance.addPostFrameCallback to delay the call. 
    Ensure MediaQuery.of(context) is only called inside a build method of a widget that is a descendant of MaterialApp or WidgetsApp. If needed in initState, use WidgetsBinding.instance.addPostFrameCallback to delay the call.
  2. 90% success Pass MediaQuery data as a parameter to widgets that need it, rather than calling MediaQuery.of(context) inside them. 
    Pass MediaQuery data as a parameter to widgets that need it, rather than calling MediaQuery.of(context) inside them.

中文步骤

  1. 确保 MediaQuery.of(context) 仅在 MaterialApp 或 WidgetsApp 后代的 build 方法中调用。如果在 initState 中需要，使用 WidgetsBinding.instance.addPostFrameCallback 延迟调用。
  2. 将 MediaQuery 数据作为参数传递给需要它的 widget，而不是在其中调用 MediaQuery.of(context)。

Dead Ends

Common approaches that don't work:

  1. Adding MediaQuery.of(context) directly in main() before runApp() 100% fail

    The context from runApp() is not available; MediaQuery is only set up after the MaterialApp widget is built.

  2. Using a global variable to store MediaQuery data before the widget tree is built 90% fail

    MediaQuery depends on the widget tree context; it cannot be accessed outside the build method or before the tree is established.