Flutter

Question

我想在 Flutter application 中每次页面更改时运行一个函数。

理想情况下，我不想在每个页面的 initState 中调用此函数，因为有时人们会忘记在新页面中添加调用。

将其视为 middleware - 基本上是在页面加载之前等，一些代码需要运行。

更新代码以供审核

import 'package:flutter/material.dart';
import 'package:flutter_secure_storage/flutter_secure_storage.dart';
import 'package:myapp/pages/login_page.dart';
import 'package:myapp/pages/dashboard_page.dart';
import 'package:myapp/styles/constants.dart';
import 'package:myapp/services/auth_service.dart';

Future<void> main() async {
  // create a auth service instance
  AuthService authService = AuthService(secureStorage: FlutterSecureStorage());
  bool isLoggedIn = await authService.isUserLoggedIn();

  // run the app
  runApp(MyApp(
    isLoggedIn: isLoggedIn,
  ));
}

class MyApp extends StatefulWidget {
  final bool isLoggedIn;

  MyApp({this.isLoggedIn});

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

class _MyAppState extends State<MyApp> with RouteAware {
  final RouteObserver<PageRoute> routeObserver = RouteObserver<PageRoute>();

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    routeObserver.subscribe(this, ModalRoute.of(context));
  }

  @override
  void dispose() {
    routeObserver.unsubscribe(this);
    super.dispose();
  }

  @override
  void didPush() {
    print('didPush');
  }

  @override
  void didPopNext() {
    print('didPopNext');
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'App NAME',
      theme: ThemeData(
        primarySwatch: Colors.green,
        primaryColor: kPrimeColour,
      ),
      home: widget.isLoggedIn == true ? DashboardPage() : LoginPage(),
      navigatorObservers: [routeObserver],
    );
  }
}

Answer 1

可以使用实现方法didChangeDependencies这个函数在initState之后调用，

颤动文档：

Subclasses rarely override this method because the framework always calls build after a dependency changes. Some subclasses do override this method because they need to do some expensive work (e.g., network fetches) when their dependencies change, and that work would be too expensive to do for every build.

Link

    @override
    void didChangeDependencies() {
      super.didChangeDependencies();
      // set your stuff here 
      }

Answer 2

可以使用继承

abstract class MyState<T extends StatefulWidget> extends State {
  @override
  void initState() {
    super.initState();
    //YOUR CHANGE PAGE METHOD HERE
  }
}

class YellowBird extends StatefulWidget {
  const YellowBird({ Key key }) : super(key: key);

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

class _YellowBirdState extends MyState<YellowBird> {
  @override
  Widget build(BuildContext context) {
    return Container(color: const Color(0xFFFFE306));
  }
}

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