NoSuchMethodError：方法“ ancestorStateOfType”在null上调用 [英] NoSuchMethodError: The method 'ancestorStateOfType' was called on null

问题描述

我正在像这样的流媒体列表进行屏幕更改，当它发出时，我会更改屏幕

i am doing screen change like this iam listing for stream and when it emit i change the screen

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

     appBloc.error.listen((data) {
     _scaffoldKey.currentState.showSnackBar(new SnackBar(content: new 
        Text(data)));
    });

     appBloc.success.listen((_) => goToDashBoardScreen(context));

}

和doToDashBoardScreen看起来像这样

and doToDashBoardScreen look like this

Navigator.pushReplacement(context, new SlideRightRoute(widget: 
DashBoardScreen()));

但是我遇到这样的错误，但是我改变了页面。

but i am getting error like this but i change the page.

22:05:02.446 3 info flutter.tools E/flutter (13216): NoSuchMethodError: 
The method 'ancestorStateOfType' was called on null.
22:05:02.446 4 info flutter.tools E/flutter (13216): Receiver: null
22:05:02.446 5 info flutter.tools E/flutter (13216): Tried calling: 
ancestorStateOfType(Instance of 'TypeMatcher<NavigatorState>')
22:05:02.446 6 info flutter.tools E/flutter (13216): #0      
Object.noSuchMethod (dart:core/runtime/libobject_patch.dart:48:5)
22:05:02.446 7 info flutter.tools E/flutter (13216): #1      
Navigator.of (package:flutter/src/widgets/navigator.dart:1270:19)
22:05:02.446 8 info flutter.tools E/flutter (13216): #2      
Navigator.pushReplacement 
(package:flutter/src/widgets/navigator.dart:952:22)

推荐答案

您的窗口小部件最有可能从树上移开。因此，它不再有上下文。

Your widget has most likely been removed from the tree. Therefore it doesn't have a context anymore.

问题是，您忘记了退订流。因此，即使将其从树中删除后，您的小部件仍会尝试更新。

The problem being, you forgot to unsubscribe to your Stream. Therefore even after being removed from the tree, your widget still attempts to update.

一种解决方案是取消对处置的认购：

A solution would be to unsubscribe on dispose call:

class Foo extends StatefulWidget {
  @override
  _FooState createState() => _FooState();
}

class _FooState extends State<Foo> {
  StreamSubscription streamSubscription;

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

    streamSubscription = Bloc.of(context).myStream.listen((value) {
      print(value);
    });
  }

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

  @override
  Widget build(BuildContext context) {
    return Container();
  }
}

这篇关于NoSuchMethodError：方法“ ancestorStateOfType”在null上调用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！