Flutter：防止 Future Builder 被触发

Question

我是 flutter 的新手，我正在尝试构建一个简单的应用程序。 每当我从 EditProfileScreen 更新配置文件详细信息并尝试通过 LandingScreen 返回到 ProfileScreen 时，FutureBuilder 都会继续触发并出现 LogoScreen。 如何避免这种情况？

我尝试使用 Navigator pop，但在这种情况下我的新数据没有更新。 我无法直接导航到 ProfileScreen，因为我不想松开底部导航栏。 有人可以建议我这样做的正确方法吗？

登陆屏幕（）：

class LandingScreen extends StatefulWidget {
  final int index;

  LandingScreen({this.index});

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

class _LandingScreenState extends State<LandingScreen> {
  int _currentIndex = 0;
  List<Futsal> list;
  List<Search> listHistory;
  List<Futsal> futsalList;
  Future<dynamic> loadDataFuture;

  final List<Widget> _children = [
    HomePage(),
    ExploreScreen(),
    ProfileDetails(),
  ];

  @override
  void initState() {
    onTappedBar(widget.index);
    loadDataFuture = getFutureData();
    super.initState();
  }

  void onTappedBar(int index) {
    setState(() {
      _currentIndex = index;
    });
  }

  Future getFutureData() async {
      listHistory = await fetchSearchs();
      futsalList = await fetchFutsals();
  }

  @override
  Widget build(BuildContext context) {
    return SafeArea(
      child: new FutureBuilder(
        future: loadDataFuture, 
        builder: (context, snapshot) {
          switch (snapshot.connectionState) {
            case ConnectionState.none:
        
              return new Text('Please close the application and Try Again.');
            case ConnectionState.waiting:
              return LogoScreen();
            default:
              if (snapshot.hasError)
                return new Text('Error: ${snapshot.error}');
              else
                return Scaffold(
                  backgroundColor: Colors.white,
                  appBar: new AppBar(
                    automaticallyImplyLeading: false,
                    backgroundColor: kPrimaryLightColor,
                    title: Text(
                      'letsfutsal',
                      style: TextStyle(
                        fontWeight: FontWeight.bold,
                        color: kPrimaryColor,
                      ),
                    ),
                    actions: <Widget>[
                      IconButton(
                        icon: Icon(Icons.search),
                        color: kPrimaryColor,
                        onPressed: () {
                          showSearch(
                              context: context,
                              delegate: SearchScreen(
                                  futsalList: futsalList,
                                  listHistory: listHistory));
                        },
                      ),
                    ],
                  ),
                  body: _children[_currentIndex],
                  bottomNavigationBar: BottomNavigationBar(
                    onTap: onTappedBar,
                    currentIndex: _currentIndex,
                    selectedItemColor: kPrimaryColor,
                    unselectedItemColor: Colors.black38,
                    showSelectedLabels: false,
                    showUnselectedLabels: false,
                    items: [
                      BottomNavigationBarItem(
                        icon: new FaIcon(FontAwesomeIcons.home),
                        title: new Text(''),
                      ),
                      BottomNavigationBarItem(
                        icon: FaIcon(FontAwesomeIcons.safari),
                        title: Text(''),
                      ),
                      BottomNavigationBarItem(
                        icon: FaIcon(FontAwesomeIcons.solidUserCircle),
                        title: Text(''),
                      ),
                    ],
                  ),
                );
          }
        },
      ),
    );
  }
}

配置文件屏幕（）：

class ProfileDetails extends StatelessWidget {
@override
  Widget build(BuildContext context) {
    return MultiProvider(
      providers: [
        ChangeNotifierProvider(create: (context) => CustomUserProvider()),
        ChangeNotifierProvider(create: (context) => MyBookingsProvider()),
      ],
      child: SafeArea(
        child: Scaffold(
          backgroundColor: kPrimaryLightColor,
          appBar: new AppBar(
            automaticallyImplyLeading: false,
            elevation: 0,
            title: Text(
              'Profile',
              style: TextStyle(
                fontWeight: FontWeight.bold,
                color: kPrimaryColor,
              ),
            ),
            actions: [
              FlatButton.icon(
                onPressed: () {},
                icon: Icon(
                  FontAwesomeIcons.signOutAlt,
                  color: kPrimaryColor,
                ),
                label: Text(
                  'Log Out',
                  style: TextStyle(
                    color: kPrimaryColor,
                  ),
                ),
              ),
            ],
          ),
          body: new Container(
            padding: const EdgeInsets.all(15.0),
            child: new Center(
              child: new Column(
                children: <Widget>[
                  UserDetails(),
                  MyBookingsList(),
                ],
              ),
            ),
          ),
        ),
      ),
    );
  }
}

class UserDetails extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    Size size = MediaQuery.of(context).size;
    final userProvider = Provider.of<CustomUserProvider>(context);

    if (userProvider.user.length == 0) {
      return Container();
    } else {
      return Column(
        children: <Widget>[
          new CircularImageContainer(
            radius: 50,
            imageUrl: "assets/images/profile.png",
          ),
          SizedBox(height: size.height * 0.03),
          Text(
            userProvider.user[0].name != null ? userProvider.user[0].name : "",
            style: TextStyle(
              fontWeight: FontWeight.bold,
              fontSize: 18.0,
            ),
          ),
          SizedBox(height: size.height * 0.01),
          Text(
            userProvider.user[0].address != null
                ? userProvider.user[0].address
                : "",
          ),
          FlatButton.icon(
            onPressed: () {
              Navigator.push(
                context,
                MaterialPageRoute(
                  builder: (context) {
                    return EditProfileScreen(
                      user: userProvider.user[0],
                    );
                  },
                ),
              );
            },
            icon: Icon(
              Icons.edit,
              color: kPrimaryColor,
            ),
            label: Text(
              'Edit Profile',
              style: TextStyle(
                color: kPrimaryColor,
              ),
            ),
          ),
        ],
      );
    }
  }
}

class MyBookingsList extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    Size size = MediaQuery.of(context).size;
    final bookingsProvider = Provider.of<MyBookingsProvider>(context);
    if (bookingsProvider.bookings.length == 0) {
      return Container();
    } else {
      return Column(
        children: <Widget>[
          ScrollListContainer(
            text: "My Bookings",
            size: size,
          ),
          ListView.builder(
            shrinkWrap: true,
            itemCount: bookingsProvider.bookings.length,
            scrollDirection: Axis.vertical,
            physics: BouncingScrollPhysics(),
            itemBuilder: (BuildContext context, int index) {
              return Card(
                child: Container(
                  width: 150,
                  child: ExpansionTile(
                    title: Text(
                      index.toString() +
                                  '. ' +
                                  bookingsProvider
                                      .bookings[index].futsal.customUser.name !=
                              null
                          ? bookingsProvider
                              .bookings[index].futsal.customUser.name
                          : "",
                      style: TextStyle(
                        fontSize: 15.0,
                        fontWeight: FontWeight.bold,
                        color: Colors.black,
                      ),
                    ),
                    children: <Widget>[
                      ListTile(
                        title: Text(
                          bookingsProvider.bookings[index].status,
                        ),
                        subtitle: Text(
                          'For ' + bookingsProvider.bookings[index].bookedFor,
                        ),
                        dense: true,
                      ),
                    ],
                  ),
                ),
              );
            },
          ),
        ],
      );
    }
  }
}

编辑配置文件屏幕（）：

class EditProfileScreen extends StatefulWidget {
  final CustomUser user;

  EditProfileScreen({this.user});

  @override
  _EditProfileScreenState createState() => new _EditProfileScreenState();
}

class _EditProfileScreenState extends State<EditProfileScreen> {
  final scaffoldKey = new GlobalKey<ScaffoldState>();
  final formKey = new GlobalKey<FormState>();

  String _name;
  String _address;


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

  @override
  void dispose() {
    super.dispose();
  }

  void _submit() {
    final form = formKey.currentState;

    if (form.validate()) {
      form.save();

      performUpdate();
    }
  }



  void performUpdate() async {
    Map data = {
      'name': _name,
      'address': _address,
    };

    var url =MY_URL;
    var response = await http.post(url,
        headers: {"Accept": "application/json"}, body: data);
    print(response.body);

    if (response.statusCode == 200) {
      Navigator.pushReplacement(context,
          MaterialPageRoute(builder: (BuildContext context) => LandingScreen(index: 2,)));

    } 
  }

  @override
  Widget build(BuildContext context) {
    Size size = MediaQuery.of(context).size;

    return new SafeArea(
      child: Scaffold(
        key: scaffoldKey,
        backgroundColor: Colors.white,
        appBar: AppBar(
          centerTitle: true,
          // automaticallyImplyLeading: false,
          leading: BackButton(
            color: kPrimaryColor,
          ),
          elevation: 0,
          backgroundColor: kPrimaryLightColor,
          title: Text(
            widget.user.name,
            style: TextStyle(
              fontWeight: FontWeight.bold,
              color: kPrimaryColor,
            ),
          ),
        ),
        body: new Container(
          height: size.height,
          width: double.infinity,
          padding: const EdgeInsets.all(30.0),
          child: SingleChildScrollView(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                Text(
                  "Edit Details",
                  style: TextStyle(fontWeight: FontWeight.bold),
                ),
                SizedBox(height: size.height * 0.03),
                new Form(
                  key: formKey,
                  child: new Column(
                    children: <Widget>[
                      new TextFieldContainer(
                        child: new TextFormField(
                          controller:
                              TextEditingController(text: widget.user.name),
                          decoration: new InputDecoration(
                            labelText: "Name",
                            icon: Icon(
                              Icons.person,
                              color: kPrimaryColor,
                            ),
                            border: InputBorder.none,
                          ),
                          validator: (val) =>
                              val.isEmpty ? 'Please enter name' : null,
                          onSaved: (val) => _name = val,
                        ),
                      ),
                      new TextFieldContainer(
                        child: new TextFormField(
                          controller: TextEditingController(
                              text: widget.user.address != null
                                  ? widget.user.address
                                  : ''),
                          decoration: new InputDecoration(
                            labelText: "Address",
                            icon: Icon(
                              Icons.email,
                              color: kPrimaryColor,
                            ),
                            border: InputBorder.none,
                          ),
                          validator: (val) =>
                              val.isEmpty ? 'Please enter your address' : null,
                          onSaved: (val) => _address = val,
                        ),
                      ),
                      RoundedButton(
                        text: "Update",
                        press: _submit,
                      ),
                    ],
                  ),
                ),
              ],
            ),
          ),
        ),
      ),
    );
  }
}

Answer 1

当您使用 Provider 时，您可以执行以下操作。

 @override
 void initState() {
bloc = Provider.of<MyDealsBLOC>(context, listen: false);
if (!bloc.isLoaded) {
  Future.delayed(
    Duration.zero,
    () => Provider.of<MyDealsBLOC>(context, listen: false).loadData(),
  );
  bloc.isLoaded = true;
  print('IsLoaded: ${bloc.isLoaded}');
}

super.initState();
}

我所做的是在我的块中使用布尔值 isLoaded 来检查数据是否已加载一次。 我相信你也可以这样做。

Answer 2

如果您试图阻止网络图像继续下载和加载，您需要使用cached_network_image来缓存图像并且它不会再次下载。 只需输入图像下载 URL，软件包将完成剩下的工作。