Question

我有一个“开始”和“停止”按钮，并且当前状态为就绪或未就绪。我想要的行为是：

按下开始按钮时状态尚未就绪，仅在按下停止按钮4秒钟后才处于就绪状态。如果在这4秒钟内按下启动按钮，我希望在停止功能将其设置为就绪后状态立即变为“未就绪”（因此本质上启动功能应等待停止功能完成）。

这是我尝试用来解决此问题的示例应用程序：

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: HomePage(),
    );
  }
}

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        crossAxisAlignment: CrossAxisAlignment.stretch,
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          Text(
            isCurrentlyReady ? "ready" : "not ready",
            textAlign: TextAlign.center,
          ),
          if (canPressStart)
            CupertinoButton(
              child: Text('Start'),
              onPressed: start,
            )
          else
            CupertinoButton(
              child: Text('Stop'),
              onPressed: stop,
            )
        ],
      ),
    );
  }

  bool isCurrentlyReady = true;
  bool canPressStart = true;

  Future<bool> isReadyFuture = Future.value(true);

  start() async {
    setState(() {
      canPressStart = false;
    });
    await isReadyFuture;
    setState(() {
      isCurrentlyReady = false;
    });
    //this future will never come
    isReadyFuture = Future.delayed(Duration(days: 90000), () => true);
  }

  stop() async {
    setState(() {
      canPressStart = true;
    });
    await Future.delayed(Duration(seconds: 4));
    setState(() {
      isCurrentlyReady = true;
    });
    isReadyFuture = Future.value(true);
  }
}

我如何实现期望的行为？

Answer 1

您在这里：https://codepen.io/gazialankus/pen/NWGMYEe

SO也需要该代码。此处：

  Object token;
  bool isReady = false;

  void onStart() {
    setState(() {
      isReady = false;
    });
    token = null;
  }

  Future<void> onStop() async {
    Object myToken = Object();
    token = myToken;
    await Future.delayed(Duration(seconds: 4));
    if (token == myToken) {
      setState(() {
        isReady = true;
      });
      token = null;
    }
  }

Flutter / Dart如何让一个功能等待另一个独立功能完成？

1 个答案: