NoSuchMethodError：使用等待和异步方法在null上调用了方法'ancestorStateOfType' [英] NoSuchMethodError: The method 'ancestorStateOfType' was called on null with await and async method

问题描述

我想创建一个加载器数据，最后，屏幕加载的数据将自动更改屏幕（使用导航器）。

i would like to create a loader data, at the end the load of the data the screen will automaticly change the screen (with Navigator).

但是我有

Unhandled Exception: NoSuchMethodError: The method 'ancestorStateOfType' was called on null.

在方法 getDataOfUser（）的末尾， print（a）执行得很好，但是当它尝试更改屏幕时会崩溃，并且出现此错误：

At the end of the method "getDataOfUser()" the "print(a)" executed fine but when it try to change the screen it crash and i have this error :

E/flutter (32148): [ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: NoSuchMethodError: The method 'ancestorStateOfType' was called on null.
E/flutter (32148): Receiver: null
E/flutter (32148): Tried calling: ancestorStateOfType(Instance of 'TypeMatcher<NavigatorState>')
E/flutter (32148): #0      Object.noSuchMethod (dart:core-patch/object_patch.dart:50:5)
E/flutter (32148): #1      Navigator.of (package:flutter/src/widgets/navigator.dart:1446:19)
E/flutter (32148): #2      LoginScreenPresenter.initState.<anonymous closure> (package:test_app/login_presenter.dart:35:17)

class loginPresenter extends StatefulWidget {
  Vendeur v;
  loginPresenter({Key key, this.v}) : super(key: key);

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

class LoginScreenPresenter extends State<loginPresenter> {
  RestDatasource api = new RestDatasource();

  BuildContext context;

  bool finish = false;

  @override
  void initState() {
    getDataOfUser(widget.v).then((a) {
      print(a)
      Navigator.of(context).pushReplacement(new MaterialPageRoute(
          builder: (BuildContext context) => HomePage(
                v: widget.v,
              )));
    });

    super.initState();
  }

  Future<bool> getDataOfUser(Vendeur user) async {

    await api.getRegionsFromUser(user.idV).then((list) async {
      if (list != null) {
        for (var i = 0; i < list.length; ++i) {
          await DBProvider.db.newRegion(list[i], 1);
        }
      }
    });

    await api.getClientsFromUser(user.idV).then((list) async {
      if (list != null) {
        for (var i = 0; i < list.length; ++i) {
          await DBProvider.db.newClient(list[i], 1);
        }
      }
    });

    await api.getInterlocuteursFromUser(user.idV).then((list) async {
      if (list != null) {
        for (var i = 0; i < list.length; ++i) {
          await DBProvider.db.newInterlocuteurs(list[i], 1);
        }
      }
    });

    await api.getVisitesFromUser(user.idV).then((list) async {
      if (list != null) {
        for (var i = 0; i < list.length; ++i) {
          await DBProvider.db.newVisite(list[i], 1);
        }
      }
    });

    await api.getAvoirsFromUser(user.idV).then((list) async {
      if (list != null) {
        for (var i = 0; i < list.length; ++i) {
          if (list[i].deleted == 0) {
            await DBProvider.db.newAvoir(list[i], 1);
          }
        }
      }
    });

    await api.getRapportsFromUser(user.idV).then((list) async {
      if (list != null) {
        for (var i = 0; i < list.length; ++i) {
          await DBProvider.db.newRapport(list[i], user);
        }
      }
    });

    return true;
  }

  @override
  Widget build(context) {
    return RaisedButton(
      onPressed: () {
        Navigator.push(
            context,
            SlideRightRoute(
                widget: HomePage(
              v: widget.v,
            )));
      },
      child: Text('go'),
    );

  }

}

推荐答案

您的上下文从未分配。您正在使用仍为空的上下文调用Navigator。

Your context was never assigned. You are calling Navigator using that context while it is still null. Try to assign it with the context from the page when it is built.

@override
Widget build(context) {
  setState(() => this.context = context);
  ...
}

这篇关于NoSuchMethodError：使用等待和异步方法在null上调用了方法'ancestorStateOfType'的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！