Question

在我的应用中，我有一个登录屏幕和一个主屏幕。从登录名导航到主屏幕时，我从.txt文件读取数据并显示4个随机数据点。我正在从initState的文件中获取数据，以便在状态更改时不会多次调用该数据，然后使用诸如...等未来的构建器等待它。

class _HomeScreenState extends State<HomeScreen> {
  Future<bool> _future;

  @override
  initState() {
    super.initState();
    print('in initState about to call _getData');
    _future = _getData();
  }

  @override
  Widget build(BuildContext context) {
    var futureBuilder = new FutureBuilder(
      future: _future,
      builder: (BuildContext context, AsyncSnapshot snapshot) {
        switch (snapshot.connectionState) {
          case ConnectionState.none:
          case ConnectionState.active:
          case ConnectionState.waiting:
            return new Center(
              child: new CircularProgressIndicator(),
            );
          case ConnectionState.done:
            if (snapshot.hasError) {
              return new Center(
                child: Text('Error'),
              );
            } else {
              return new ListView(
                children: <Widget>[
                  //my view
                ],
              );
            }
          }
        }
    );
    return MaterialApp(
        home: WillPopScope(
          onWillPop: () async {
            return Navigator.pop(context);
          },
          child: Scaffold(
            body: futureBuilder,
          ),
        )
    );

现在，当我使用“后退”按钮导航回到登录屏幕，然后返回主屏幕时，initState将关闭多次（这可以通过我留下的打印语句看到）。当您在这两个屏幕（弹出式主屏幕，推式主屏幕）之间来回移动时，initState将被指数级调用多次。我很困惑，我们将不胜感激！

编辑：登录和主屏幕的完整代码都可以找到https://github.com/ViscousOx/Flutter-Stuff

Answer 1

尝试：有效 在ConnectionState.waiting中使用默认语句。

class _HomeScreenState extends State<HomeScreen> {
  Future<bool> _future;

  @override
  initState() {
    super.initState();
    print('in initState about to call _getData');
    _future = _getData();
  }

  @override
  Widget build(BuildContext context) {
    var futureBuilder = new FutureBuilder(
      future: _future,
      builder: (BuildContext context, AsyncSnapshot snapshot) {
        switch (snapshot.connectionState) {
          case ConnectionState.waiting:
            return new Center(
              child: new CircularProgressIndicator(),
            );
          default:
            if (snapshot.hasError) {
              return new Center(
                child: Text('Error'),
              );
            } else {
              return new ListView(
                children: <Widget>[
                  //my view
                ],
              );
            }
          }
        }
    );
    return MaterialApp(
        home: WillPopScope(
          onWillPop: () async {
            return Navigator.pop(context);
          },
          child: Scaffold(
            body: futureBuilder,
          ),
        )
    );

Answer 2

可以避免连接等待状态。我曾经是：

FutureBuilder(future: _isUserLoggedIn(),
                     builder: (ctx, loginSnapshot) => 
                      loginSnapshot.data == true ?  AppLandingScreen() : SignUpScreen()
                ),

多次调用initState

2 个答案: