flutter 报错 No MediaQuery widget ancestor found.

报错如图

问题代码

import 'package:flutter/material.dart';

void main() {
    
  runApp(SampleAppPage());
}

class SampleAppPage extends StatefulWidget {
    
  const SampleAppPage({
    Key? key}) : super(key: key);

  @override
  _SampleAppPageState createState() => _SampleAppPageState();
}

class _SampleAppPageState extends State<SampleAppPage>
    with SingleTickerProviderStateMixin {
    
  late AnimationController controller;
  late CurvedAnimation curve;

  @override
  void initState() {
    
    super.initState();
    controller = AnimationController(
      duration: const Duration(milliseconds: 2000),
      vsync: this,
    );
    curve = CurvedAnimation(
      parent: controller,
      curve: Curves.easeIn,
    );
  }

  @override
  Widget build(BuildContext context) {
    
    return Scaffold(
      body: Center(
        child: GestureDetector(
          child: RotationTransition(
            turns: curve,
            child: const FlutterLogo(size: 200.0),
          ),
          onDoubleTap: () {
    
            if (controller.isCompleted) {
    
              controller.reverse();
            } else {
    
              controller.forward();
            }
          },
        ),
      ),
    );
  }
}

原因： flutter 界面的根组件必须是MaterialApp

修复之后的代码

import 'package:flutter/material.dart';

void main() {
    
  runApp(SampleApp());
}

class SampleApp extends StatelessWidget {
    
  // This widget is the root of your application.
  const SampleApp({
    Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    
    return const MaterialApp(
      title: 'Sample App',
      home: SampleAppPage(),
    );
  }
}

class SampleAppPage extends StatefulWidget {
    
  const SampleAppPage({
    Key? key}) : super(key: key);

  @override
  _SampleAppPageState createState() => _SampleAppPageState();
}

class _SampleAppPageState extends State<SampleAppPage>
    with SingleTickerProviderStateMixin {
    
  late AnimationController controller;
  late CurvedAnimation curve;

  @override
  void initState() {
    
    super.initState();
    controller = AnimationController(
      duration: const Duration(milliseconds: 2000),
      vsync: this,
    );
    curve = CurvedAnimation(
      parent: controller,
      curve: Curves.easeIn,
    );
  }

  @override
  Widget build(BuildContext context) {
    
    return Scaffold(
      body: Center(
        child: GestureDetector(
          child: RotationTransition(
            turns: curve,
            child: const FlutterLogo(size: 200.0),
          ),
          onDoubleTap: () {
    
            if (controller.isCompleted) {
    
              controller.reverse();
            } else {
    
              controller.forward();
            }
          },
        ),
      ),
    );
  }
}