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import 'dart:async'; import 'package:flutter/cupertino.dart'; import 'package:flutter/material.dart'; void main() => runApp(const MyApp()); class MyApp extends StatelessWidget { const MyApp({Key? key}) : super(key: key); // This widget is the root of your application. @override Widget build(BuildContext context) { return MaterialApp( title: 'Flutter Demo', theme: ThemeData( primarySwatch: Colors.blue, ), home: Scaffold( appBar: AppBar( title: const Text('倒计时'), ), body: const MyHomePage(), )); } } class MyHomePage extends StatefulWidget { const MyHomePage({Key? key}) : super(key: key); @override State<MyHomePage> createState() => _MyHomePageState(); } class _MyHomePageState extends State<MyHomePage> { late Duration time; var seconds = 0; Timer? countdownTimer; @override Widget build(BuildContext context) { return Center( child: Column( children: <Widget>[ ElevatedButton( child: const Text('定时'), onPressed: () { showCupertinoModalPopup<void>( context: context, builder: (BuildContext context) { return Container( height: 200, color: CupertinoColors.white, child: DefaultTextStyle( style: const TextStyle( color: CupertinoColors.black, fontSize: 22.0, ), child: CupertinoTimerPicker( //initialTimerDuration: time, //minuteInterval: 5, mode: CupertinoTimerPickerMode.ms, onTimerDurationChanged: (Duration newTimer) { setState(() { time = newTimer; seconds = time.inSeconds; // flag = true; }); }, ), )); }, ); }, ), ElevatedButton( child: const Text('开始倒计时'), onPressed: () { if (countdownTimer != null) { return; } countdownTimer = Timer.periodic(const Duration(seconds: 1), (timer) { setState(() { if (seconds > 0) { seconds--; } else { countdownTimer?.cancel(); countdownTimer = null; } }); }); }, ), Text( '倒计时： $seconds 秒', style: const TextStyle(fontSize: 30), ), ], ), ); } @override void dispose() { countdownTimer?.cancel(); countdownTimer = null; super.dispose(); } } |
日期: 2022 年 7 月 5 日
Flutter : LateInitializationError: Field ‘data’ has not been initialized
You don’t want a late variable, you want a nullable one. If you need to check if something is initialized, you should be using a nullable variable instead and your code is already set up to check for null
just change
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late MyData data; |
to
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MyData? data; |
E.g.
change to
参考链接
Flutter : LateInitializationError: Field ‘data’ has not been initialized, got error