在 InitState 未处理异常中显示对话框：查找已停用小部件的祖先是不安全的

Question

第一次出现屏幕时，我想检查是否启用了用户 GPS 并授予了位置权限。然后，如果其中一个不满足，我会显示对话框以打开应用设置。

源代码

_initPermission(BuildContext context) async {
    final geolocationStatus = await commonF.getGeolocationPermission();
    final gpsStatus = await commonF.getGPSService();
    if (geolocationStatus != GeolocationStatus.granted) {
      showDialog(
        context: context,
        builder: (ctx) {
          return commonF.showPermissionLocation(ctx);
        },
      );
    } else if (!gpsStatus) {
      showDialog(
        context: context,
        builder: (ctx) {
          return commonF.showPermissionGPS(ctx);
        },
      );
    }
  }

然后我在 initState 中这样调用这个函数：

初始化状态

void initState() {
    super.initState();
    Future.delayed(Duration(milliseconds: 50)).then((_) => _initPermission(context));
  }

问题是，每次屏幕出现时都会给我这样的错误：

错误

[ERROR:flutter/lib/ui/ui_dart_state.cc(166)] Unhandled Exception: Looking up a deactivated widget's ancestor is unsafe.
At this point the state of the widget's element tree is no longer stable.
To safely refer to a widget's ancestor in its dispose() method, save a reference to the ancestor by calling dependOnInheritedWidgetOfExactType() in the widget's didChangeDependencies() method.

我做了什么：

• 像这样改变 InitState

//1
 WidgetsBinding.instance.addPostFrameCallback((_) {
      _initPermission(context);
 });
//2
  SchedulerBinding.instance.addPostFrameCallback((_) => _initPermission(context));
//3
Timer.run(() { 
      _initPermission(context); 
  })

• 为脚手架添加全局键

final GlobalKey<ScaffoldState> _scaffoldKey = GlobalKey<ScaffoldState>();
 Scaffold(
        key: _scaffoldKey,

• 搜索与我类似的问题
  1. Show Dialog In Initstate
  2. Looking up a deactivated widget's ancestor is unsafe
  3. Load Data In Initstate

我做的结果什么都没有，第一次出现的时候还是出现错误。

但奇怪的是，这只发生在第一次出现屏幕时。当我执行 热重启 时，错误消息消失了。

[第一次出现屏幕失败]

[热重启，错误消失]

Answer 1

我没有办法测试它（我没有 GPS 包）但尝试改变

Future.delayed(Duration(milliseconds: 50)).then((_) => _initPermission(context));

到

Future.delayed(Duration(milliseconds: 50)).then((_) => _initPermission()); //this inside the initstate

_initPermission() async{
final geolocationStatus = await commonF.getGeolocationPermission();
final gpsStatus = await commonF.getGPSService();
if (geolocationStatus != GeolocationStatus.granted) {
  await showDialog(
    context: context,
    builder: (ctx) => commonF.showPermissionLocation
    },
  );
} else if (!gpsStatus) {
  await showDialog(
    context: context,
    builder: (ctx) => commonF.showPermissionGPS
    },
  );
}
} // the stateful widget can use the context in all its methods without passing it as a parameter

错误在热启动中消失，因为它只是刷新小部件的状态，但它已经创建（如果您进行热启动并在 initState 中打印一些内容，例如 print('This is init');，你不会看到它要么是因为刷新没有处理和初始化小部件，所以它不会再次运行那段代码）

编辑

根据您的要点，我只是做了一个可重现的最小示例，并在 DartPad 中运行没有问题，稍后我将在 VS 上尝试，但现在您可以检查是否有任何不同

enum GeolocationStatus{granted, denied} //this is just for example

class MyWidget extends StatefulWidget {
  @override
  _MyWidgetState createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {


showPermissionGPS() {
    return AlertDialog(
        title: Text('GPSStatus'),
      );
  }

  _showPermissionLocation() {
    return AlertDialog(
        title: Text('Permission Localization'),
      );
  }

  @override
  initState(){
    super.initState();
    Future.delayed(Duration(milliseconds: 50)).then((_) => _initPermission());
  }


_initPermission() async{
  final geolocationStatus = await Future<GeolocationStatus>.value(GeolocationStatus.granted); //mocked future with a response to test
  final gpsStatus = await Future<bool>.value(false); //mocked future with a response to test
  if (geolocationStatus != GeolocationStatus.granted) {
   await showDialog(
      context: context,
      builder: (ctx) => _showPermissionLocation() //this mock commonF.showPermissionLocation and returns an AlertDialog
   );
  } else if (!gpsStatus) {
   await showDialog(
    context: context,
    builder: (ctx) => _showPermissionGPS() //this mock commonF.showPermissionGPS and returns an AlertDialog
  );
 }
}

  @override
  Widget build(BuildContext context) {
    return Text('My text');
  }
}