如何从Flutter（Dart）中的另一个类调用方法？

Question

我创建了一个主页，并且该用户可以登录该应用程序，在下一个屏幕中，用户可以看到他们的个人资料信息（仅限个人资料名称），并在其下面是他们的signOut按钮。用户可以使用signOut按钮从应用程序中签名。但它不适合我。

我想通过在details.dart中按signOut按钮从main.dart调用signOut方法（两个类都在不同的文件中）

但是当我在详细信息中按下Sign Out按钮时。没有任何反应！

代码如下：

main.dart

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:google_sign_in/google_sign_in.dart';
import 'details.dart';

void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      debugShowCheckedModeBanner: false,
      home: new MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  MyHomePageState createState() => MyHomePageState();
}

class MyHomePageState extends State<MyHomePage> {
  final FirebaseAuth firebaseAuth = FirebaseAuth.instance;
  final  GoogleSignIn googleSignIn = GoogleSignIn();
  static bool _LoginButton = true;

  void signOut(){
    googleSignIn.signOut();
    setState((){
      _LoginButton = true;
    });
    print(_LoginButton);
    print("User Signed Out");
  }

  Future<FirebaseUser> _signIn() async{
    if(_LoginButton==true){
      setState((){
        _LoginButton=false;
      });
      GoogleSignInAccount googleSignInAccount = await googleSignIn.signIn();
      GoogleSignInAuthentication googleSignInAuthentication = await googleSignInAccount.authentication;
      FirebaseUser firebaseUser = await firebaseAuth.signInWithGoogle(idToken: googleSignInAuthentication.idToken, accessToken: googleSignInAuthentication.accessToken);
      print("Username is "+firebaseUser.displayName);
      setState((){
        _LoginButton = true;
      });
      Navigator.push(context, MaterialPageRoute(builder: (context) => details(firebaseUser.displayName,signOut)));

      return firebaseUser;
    }
  }

  bool _LoginButtonBool(){
    return _LoginButton;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("Google auth with firebase"),),
      body: Center(
        child: _LoginButtonBool()?Container(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.spaceAround,
            children: <Widget>[
              MaterialButton(onPressed: _LoginButtonBool() ? () => _signIn().then((FirebaseUser firebaseuser ) =>print(firebaseuser)).catchError((e) => print(e)): null,
              child: Text("Login"),color: Colors.orange,),
            ],
          ),
        ):CircularProgressIndicator(backgroundColor: Colors.greenAccent.withOpacity(0.01),),
      ),
    );
  }
}

details.dart

import 'package:flutter/material.dart';
import 'package:flutter_auth/main.dart';

class details extends StatelessWidget {
  String name;
  final Function callback;
  details(this.name,this.callback);
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body:Center(child: Column(
        mainAxisAlignment: MainAxisAlignment.spaceAround,
        children: <Widget>[
          Text(name),
          MaterialButton(onPressed: () => callback,
          child: Text("Log out"),color: Colors.orange),
        ],
      ),),
    );
  }
}

Answer 1

您必须小心您要执行的操作，因为您可能正在访问未安装的页面/窗口小部件。想象一下，你做了一个pushReplacement(new MaterialPageroute(...))。树中不再提供上一页，因此您无法访问它或其任何方法。

除非您的树中有明确的父子关系，否则您应该将逻辑抽象为外部或业务逻辑类。因此，您确定要调用类的活动实例。

下面是一个使用Business对象传递的示例。如果你使用其他模式，如BLOC，ScopedModel，Streams等，会更好。但为了简单起见，我认为这应该足够了。

import "package:flutter/material.dart";

void main() {
  runApp(MyApp(new Logic()));
}

class Logic {
  void doSomething() {
    print("doing something");
  }
}

class MyApp extends StatelessWidget {
  final Logic logic;

  MyApp(this.logic);

  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      home: new HomePage(widget.logic),
    );
  }
}

class HomePage extends StatelessWidget {
  final Logic logic;

  HomePage(this.logic);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: FlatButton(
          onPressed: () { Navigator.of(context).pushReplacement(
             MaterialPageRoute(
               builder: (context) => AnotherPage(logic),
             ))},
          child: Text("Go to AnotherPage"),
        ),
      ),
    );
  }
}

class AnotherPage extends StatelessWidget {
  final Logic logic;

  AnotherPage(this.logic);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: FlatButton(
          onPressed: logic.doSomething,
          child: Text("Press me"),
        ),
      ),
    );
  }
}

如果你仍然想在另一个页面中调用一个函数并且你确定页面已经安装（你已经完成了push而不是pushReplacement），你可以执行以下操作。 （小心轻放）

class HomePage extends StatelessWidget {

  HomePage();

  void onCalledFromOutside() {
    print("Call from outside");
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
    child: FlatButton(
          onPressed: () { Navigator.of(context).push(
             MaterialPageRoute(
               builder: (context) => AnotherPage(onCalledFromOutside),
             ))},
          child: Text("Go to AnotherPage"),
        ),
      ),
    );
  }
}

class AnotherPage extends StatelessWidget {
  final Function callback

  AnotherPage(this.callback);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
    child: FlatButton(
           onPressed: callback,
           child: Text("Press me"),
        ),
      ),
    );
  }
}

Answer 2

在DetailsPage中导入HomePage类并从中创建一个新实例，然后调用所需的方法（如果它是公共方法）。