如果我使用提供程序，如何在App启动时调用方法? [英] How to call method at App start if I am using provider?

问题描述

我想完成对服务器的get请求，以便在启动时获取我的应用程序的数据.我阅读了一些主题，这些主题描述了在构建窗口小部件后如何运行方法.但是所有这些都是在不使用provider时的描述情况.而且我不确定在小部件内执行此请求是否是个好主意.

I want to complete get request to server to get data for my app at it start. I read several topics that describe how to run method after building widgets. But all of them are describe situations when provider is not using. And I am not sure that it's good idea to do this request inside widget.

我尝试了几种方法，但没有成功. 这是我的代码:

I tried several approaches but did not get success. Here is my code:

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: ChangeNotifierProvider<TenderApiData>(
          builder: (_) => TenderApiData(), child: HomePage()),
    );
  }
}

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(appBar: AppBar(), body: MainContainer());
  }

}

class TenderApiData with ChangeNotifier {
  String access_token;
  List<Map<String, String>> id_names;

  String access_token_url =  "https://...";

  getApiKey() async { // I need to call this method at app start up 
    var response = await http
        .post(access_token_url, headers: {"Accept": "application/json"});
    if (response.statusCode == 200) {
      access_token = json.decode(response.body)['access_token'];
      notifyListeners();
    }
  }

}

class MyTestWidget extends StatefulWidget {
  MyTestWidgetState createState() => MyTestWidgetState();

}

class MyTestWidgetState extends State<MyTestWidget> {

  bool isKeyGetted = false;

  // before I used this when I extracted data on click event. 
  // I am not sure that it's needed now
  @override
  void didChangeDependencies() { 
    if (!isKeyGetted) {
      Provider.of<TenderApiData>(context).getApiKey();
      isKeyGetted = !isKeyGetted;
    }
    super.didChangeDependencies();
  }

  @override
  Widget build(BuildContext context) {

    if (!isKeyGetted) {
      Provider.of<TenderApiData>(context).getApiKey();
      isKeyGetted = !isKeyGetted;
    }

    var result = Provider.of<TenderApiData>(context).access_token;
    var test = Provider.of<TenderApiData>(context).id_names;
    return Column(
      children: <Widget>[
        RaisedButton(
          onPressed: Provider.of<TenderApiData>(context).getRegionsList,
          child: Text("get regions"),
        ),
      ],
    );
  }


}

class MainContainer extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return Table(
      children: [
        TableRow(children: [
          Row(
            children: <Widget>[
              Container(child: MyTestWidget()),
              Container(child: Text("Regions"),),

              Expanded(child: SelectRegions(),  )
            ],
          )
        ]),
        TableRow(children: [
          Row(
            children: <Widget>[
              Text("Label"),
              Text("Value"),
            ],
          )
        ]),
      ],
    );
  }
}

推荐答案

您可以将TenderApiData存储为MyApp的成员，在MyApp构造函数中进行启动调用，然后将现有实例传递给后代.
这是它的外观:

You can store TenderApiData as member of MyApp, make a startup call in MyApp constructor and pass existing instance to descendants.
Here is how it will look:

class MyApp extends StatelessWidget {

  final TenderApiData _tenderApiData = TenderApiData();

  MyApp() {
    _tenderApiData.getApiKey();
  };

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: ChangeNotifierProvider<TenderApiData>(
          builder: (_) => _tenderApiData, child: HomePage()),
    );
  }
}

其他类别将保持不变.

另一种选择是将TenderApiData作为构造函数参数传递到MyApp中，使其更具可测试性.

Another option would be to pass TenderApiData as constructor parameter into MyApp, making it more testable.

void main() {
  final TenderApiData tenderApiData = TenderApiData();
  tenderApiData.getApiKey(); // call it here or in MyApp constructor - now it can be mocked and tested
  runApp(MyApp(tenderApiData));
}

class MyApp extends StatelessWidget {

  final TenderApiData _tenderApiData;

  MyApp(this._tenderApiData);

// ...

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