将数据传递给 Flutter 中的有状态小部件

Question

我想知道在创建有状态小部件时向其传递数据的推荐方法是什么。

我见过的两种款式是：

class ServerInfo extends StatefulWidget {

  Server _server;

  ServerInfo(Server server) {
    this._server = server;
  }

  @override
    State<StatefulWidget> createState() => new _ServerInfoState(_server);
}

class _ServerInfoState extends State<ServerInfo> {
  Server _server;

  _ServerInfoState(Server server) {
    this._server = server;
  }
}

这个方法在ServerInfo和_ServerInfoState中都保留了一个值，有点浪费

另一种方法是使用widget._server:

class ServerInfo extends StatefulWidget {

  Server _server;

  ServerInfo(Server server) {
    this._server = server;
  }

  @override
    State<StatefulWidget> createState() => new _ServerInfoState();
}

class _ServerInfoState extends State<ServerInfo> {
  @override
    Widget build(BuildContext context) {
      widget._server = "10"; // Do something we the server value
      return null;
    }
}

这似乎有点倒退，因为状态不再存储在 _ServerInfoSate 中，而是存储在小部件中。

有这方面的最佳实践吗？

Answer 1

不要使用它的构造函数将参数传递给 State。您应该只使用 this.widget.myField.

访问参数

不仅编辑构造函数需要大量的手工工作；它没有带来任何东西。没有理由复制 Widget.

的所有字段

编辑：

这是一个例子：

class ServerIpText extends StatefulWidget {
  final String serverIP;

  const ServerIpText ({ Key? key, this.serverIP }): super(key: key);

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

class _ServerIpTextState extends State<ServerIpText> {
  @override
  Widget build(BuildContext context) {
    return Text(widget.serverIP);
  }
}

class AnotherClass extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Center(
      child: ServerIpText(serverIP: "127.0.0.1")
    );
  }
}

Answer 2

另一个答案，建立在@RémiRousselet 的答案和@user6638204 的问题上，如果你想传递初始值并仍然能够在以后的状态下更新它们：

class MyStateful extends StatefulWidget {
  final String foo;

  const MyStateful({Key key, this.foo}): super(key: key);

  @override
  _MyStatefulState createState() => _MyStatefulState(foo: this.foo);
}

class _MyStatefulState extends State<MyStateful> {
  String foo;

  _MyStatefulState({this.foo});

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

Answer 3

用于传递初始值（不向构造函数传递任何内容）

class MyStateful extends StatefulWidget {
  final String foo;

  const MyStateful({Key key, this.foo}): super(key: key);

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

class _MyStatefulState extends State<MyStateful> {
  @override
  void initState(){
    super.initState();
    // you can use this.widget.foo here
  }

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

Answer 4

最好的方法 是不要使用它的构造函数将参数传递给 State class。您可以使用 widget.myField.

在状态 class 中轻松访问

例如

class UserData extends StatefulWidget {
  final String clientName;
  final int clientID;
  const UserData(this.clientName,this.clientID);

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

class UserDataState extends State<UserData> {
  @override
  Widget build(BuildContext context) {
    // Here you direct access using widget
    return Text(widget.clientName); 
  }
}

导航屏幕时传递数据：

 Navigator.of(context).push(MaterialPageRoute(builder: (context) => UserData("WonderClientName",132)));

Answer 5

@Rémi Rousselet、@Sanjayrajsinh、@Daksh Shah 也更好。但我也定义这是从开始 point.that 哪个参数是哪个值

   import 'package:flutter/material.dart';
    
    
    void main() => runApp(MyApp());
    
    class MyApp extends StatelessWidget {
      String name = "Flutter Demo";
      String description = "This is Demo Application";
    
      @override
      Widget build(BuildContext context) {
        return MaterialApp(
          home: MainActivity(
            appName: name,
            appDescription: description,
          ),
        );
      }
    }
    
    class MainActivity extends StatefulWidget {
      MainActivity({Key key, this.appName, this.appDescription}) : super(key: key);
      var appName;
      var appDescription;
    
      @override
      _MainActivityState createState() => _MainActivityState();
    }
    
    class _MainActivityState extends State<MainActivity> {
      @override
      Widget build(BuildContext context) {
        return Scaffold(
          appBar: AppBar(
            title: Text(widget.appName),
          ),
          body: Scaffold(
            body: Center(
              child: Text(widget.appDescription),
            ),
          ),
        );
      }
    }

Answer 6

Flutter 的有状态小部件 API 有点尴尬：将数据存储在 Widget 中，以便在位于 State 对象中的 build() 方法中访问它如果您不想使用一些更大的状态管理选项（Provider、BLoC），使用 flutter_hooks (https://pub.dev/packages/flutter_hooks) - 它是 SatefullWidgets:

更好更干净的替代品

class Counter extends HookWidget {
  final int _initialCount;

  Counter(this._initialCount = 0);
  
  @override
  Widget build(BuildContext context) {
    final counter = useState(_initialCount);

    return GestureDetector(
      // automatically triggers a rebuild of Counter widget
      onTap: () => counter.value++,
      child: Text(counter.value.toString()),
    );
  }
}

Answer 7

要将data传递给有状态的小部件，首先，创建两个页面。现在从第一页打开第二页并传递数据。

class PageTwo extends StatefulWidget {
  final String title;
  final String name;

  PageTwo ({ this.title, this.name });

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

class PageTwoStateState extends State<PageTwo> {
  @override
  Widget build(BuildContext context) {
      return Text(
         widget.title,
         style: TextStyle(
               fontSize: 18, fontWeight: FontWeight.w700),
               ),
  }
}

class PageOne extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialButton(
          text: "Open PageTwo",
          onPressed: () {
                var destination = ServicePage(
                   title: '<Page Title>',
                   provider: '<Page Name>',
                );
                Navigator.push(context,
                    MaterialPageRoute(builder: (context) => destination));
                        },);
  }
}

将数据传递给 Flutter 中的有状态小部件

Passing Data to a Stateful Widget in Flutter

pass-data

dart

flutter

statefulwidget