Uncomments the code at 61, 106 or 114 will cause the error `MediaQuery.of() called with a context that does not contain a MediaQuery.`

main.dart

import 'dart:async';
import 'dart:math';
import 'package:flutter/cupertino.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/scheduler.dart';
import 'package:flutter/services.dart';
import 'views/main_view.dart';
import 'views/update_view.dart';
import 'store.dart';
import 'recordKeeper/store.dart';

final RecordKeeper<AppState> appStore = RecordKeeper<AppState>(
  AppState('http://192.168.5.52:8080'),
  AppActions()
);

void main() => runApp(App(appStore));

class LifecycleEventHandler extends WidgetsBindingObserver {
  LifecycleEventHandler({this.onResume, this.onSuspend});

  final VoidCallback onResume;
  final VoidCallback onSuspend;

  @override
  Future<Null> didChangeAppLifecycleState(AppLifecycleState state) async {
    switch (state) {
      case AppLifecycleState.inactive:
      case AppLifecycleState.paused:
      case AppLifecycleState.suspending:
        onSuspend();
        break;
      case AppLifecycleState.resumed:
        onResume();
        break;
    }
  }
}

class App extends StatefulWidget {
  final RecordKeeper<AppState> appStore;

  App(this.appStore);

  @override
  _AppState createState() => _AppState();
}

class _AppState extends State<App> {
  bool _isUpdated;

  initState() {
    super.initState();

    this._isUpdated = false;

    WidgetsBinding.instance.addObserver(
      LifecycleEventHandler(onResume: _onAppResume, onSuspend: _onAppSuspend)
    );

    // SchedulerBinding.instance.addPostFrameCallback((_) {
    //   _lockState();
    // });
  }

  void _lockState() {
    // Can't use RecordKeeperWidgetState yet so calculate
    // itTablet here manually
    MediaQueryData query = MediaQuery.of(context);
    Size size = query.size;
    double diagonal = sqrt(
      (size.width * size.width) + 
      (size.height * size.height)
    );
    bool isTablet = diagonal > 1100.0;

    if (!isTablet) {
      print('Lock screen on phones');
      SystemChrome.setPreferredOrientations([
        DeviceOrientation.portraitDown,
        DeviceOrientation.portraitUp,
      ]);
    }
  }

  void _onAppResume() {
    setState(() => this._isUpdated = false);
  }

  void _onAppSuspend() {
  }

  void _onFinishedUpdates() {
    setState(() => this._isUpdated = true);
  }

  Widget _getCurrentView() {
    if (_isUpdated) {
      return MainView();
    } else {
      return UpdateView(onFinshedUpdates: _onFinishedUpdates);
    }
  }

  // @override
  // void didChangeDependencies() { 
  //   super.didChangeDependencies();
  //   _lockState();
  // }

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    // _lockState();
    return RecordKeeperProvider(
      store: widget.appStore,
      child: CupertinoApp(
        home: _getCurrentView()
      )
    );
  }
}