Flutter：为什么我的构建器在 Web 服务调用后没有重新加载？答案

【问题标题】：Flutter : Why is my builder not getting reloaded after web service call?Flutter：为什么我的构建器在 Web 服务调用后没有重新加载？
【发布时间】：2020-09-27 13:36:16
【问题描述】：

我已经编写了 Web 服务调用，并在 initState() 方法中被调用。如果没有可用数据，则调用 CircularProgressIndicator()。但是，即使 Web 服务调用结束，进度指示器也会继续旋转！

进行服务调用后，为什么我的构建器没有重新加载？

我是新来的颤振！我哪里出错了？

    class _DashboardState extends State<Dashboard> {
      bool isLoading = false;

      Future<List<OrganizationModel>> fetchOrganizationData() async {
        isLoading = true;
        var response = await http.get(organizationAPI);          
        if (response.statusCode == 200) {
          final items = json.decode(response.body).cast<Map<String, dynamic>>();
          orgModelList = items.map<OrganizationModel>((json) {
            return OrganizationModel.fromJson(json);
          }).toList();
          isLoading = false;
          return orgModelList;
        } else {
          isLoading = false;
          throw Exception('Failed to load internet');
        }
      }

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

      @override
      Widget build(BuildContext context) {
        return Scaffold(
          appBar: AppBar(
           title: Text("Dashboard"),
        ),

        body: Container(

          decoration: BoxDecoration(
          gradient: LinearGradient(
            begin: Alignment.topCenter,
            end: Alignment.bottomCenter,
            colors: [Color(0xFF076A72), Color(0xFF64B672)])),
          child: Column(
            children: <Widget>[
              Container(
                color: Color(0xFF34A086),
                height: 1,
              ),

              isLoading ? loadProgressIndicator() : Expanded(
                child: Padding(

                  padding: const EdgeInsets.only(left: 40, right: 40),
                  child: ListView(children: <Widget>[])

                    ---my code goes here---

【问题讨论】：

标签： api web-services flutter future

【解决方案1】：

你必须调用 setState(() => isLoading = false;) 这样 Flutter 才能更新视图的状态，这样做会隐藏你的 CircularProgressIndicator。

【讨论】：

【解决方案2】：

Exception('Failed to load internet'); <-

这不是一个好主意，因为您在没有 try catch 块的情况下调用 fetchOrganizationData()

最好尝试一下：

class _DashboardState extends State<Dashboard> {
  bool isLoading = false;
  bool isFailure = false;
  List<OrganizationModel> orgModelList; // this was missing

//since your not using the return value ( it's saved in the state directly ) you could not set the return type
  fetchOrganizationData() async {
    isLoading = true;
    isFailure = false;

    var response = await http.get(organizationAPI);          
    if (response.statusCode == 200) {
      final items = json.decode(response.body).cast<Map<String, dynamic>>();
      orgModelList = items.map<OrganizationModel>((json) {
        return OrganizationModel.fromJson(json);
      }).toList();
      isFailure = false;
      // the return is not required 
    } else {
      isFailure = true;
    }
    isLoading = false;
    setState((){}); // by calling this after the whole state been set, you reduce some code lines
//setState is required to tell flutter to rebuild this widget


  }

这样你就有一个 isFailure 标志来表明在获取时是否出现问题。

【讨论】：