Flutter Future.delayed 无限循环

Question

我是运行这个代码

Future.delayed(Duration(milliseconds: 500)).then((value) => {opened = false,setState(() {}), value = "null"});

class _MyAppState extends State<MyApp> {
  @override
  Widget build(BuildContext context) {
    getStorage();
    Future.delayed(Duration(milliseconds: 500))
        .then((value) => {opened = false, setState(() {}), value = "null"});
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Container(
          color: Colors.green,
          alignment: Alignment.center,
          child: AnimatedContainer(
            duration: Duration(milliseconds: 3000),
            height: opened ? 0 : 300,
            width: opened ? 0 : 300,
            curve: Curves.fastOutSlowIn,
            alignment: Alignment.center,
            child: Lottie.asset('assets/101349-swing.json'),
          ),
        ),
      ),
    );
  }
}

它returns

I/flutter (22251): false

不断，我想避免，因为我认为它效率低下。

Answer 1

你在build方法里面添加了Future.delay，这是一个StatefullWidget，build方法可以多次调用，比如每当你调用setState()build方法就会触发并调用Future.delay 在你的情况下提供无限循环。

要调用单次，覆盖initState，你可以这样做，

  @override
  void initState() {
    super.initState();
    _initFuture();
  }

  _initFuture() async {
    Future.delayed(Duration(milliseconds: 500))
        .then((value) => {opened = false, setState(() {}), value = "null"});
  }

Flutter Future.delayed 无限循环

Flutter Future.delayed on endless loop

async-await

dart

flutter