Question

我有一个StatefulWidget类'FirstClass'，它扩展了一个状态'_FirstClassState'。从一个单独的State类，称为“ _SecondClassState”，我正在尝试访问变量的值（在“ _FirstClassState”中称为“计数器”）。

我已经找到了解决方法，但是我不确定这是否是解决问题的最佳方法。我尝试过看看其他类似的问题：

How to access Stateful widget variable inside State class outside the build method?（在StatefulWidget类中声明变量并在State类中使用“ widget”。这使我无法从“ _SecondClassState”获取“ counter”的值）
我还看过其他推荐使用GlobalKey的网站。但是，即使这可能是一个解决方案，但由于发现了其他建议尽量减少使用GlobalKeys的站点，我并没有对此做进一步的研究

second_class.dart：

import 'package:brew_crew/question/first_class.dart';
import 'package:flutter/material.dart';

class SecondClass extends StatefulWidget {
  @override
  _SecondClassState createState() => _SecondClassState();
}

class _SecondClassState extends State<SecondClass> {
  final FirstClass firstClass = FirstClass();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("MyApp"),
        centerTitle: true,
      ),
      body: Column(
        children: <Widget>[
          firstClass, //Displays the button to increase 'counter'
          FlatButton(
              child: Text("Submit"),
              onPressed: () {
                print(firstClass
                    .getCounter()); //I need to get the value of 'counter' here to use elsewhere
              }),
        ],
      ),
    );
  }
}

first_class.dart

import 'package:flutter/material.dart';

class FirstClass extends StatefulWidget {
  final _FirstClassState firstClassState = _FirstClassState();

  @override
  _FirstClassState createState() => firstClassState;

  int getCounter() {
    return firstClassState.counter;
  }
}

class _FirstClassState extends State<FirstClass> {
  int counter = 0;

  //Increases counter by 1
  void _increaseCounter() {
    setState(() {
      counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    //A button which increases counter when clicked
    return FlatButton.icon(
      icon: Icon(Icons.add),
      label: Text("Counter: $counter"),
      onPressed: () {
        _increaseCounter();
      },
    );
  }
}

如您所见，在“ FirstClass”中，我初始化了“ _FirstClassState”的新实例。在“ getCounter（）”函数中使用它，我可以获得“计数器”值。

是否有比此方法更好的方法（例如，最佳实践，更少的代码行，更易于理解的方法等）来实现我想做的事情？

Answer 1

如果绝对必须从外部访问小部件的状态，则绝对推荐使用GlobalKey。但是，在这种情况下，您不应使用任何一种方法。

_SecondClassState应该包含counter，并且您应该将其与increaseCounter函数一起作为参数传递给FirstClass。如果要增加数量，只需调用该函数即可。

遵循以下原则：

class SecondClass extends StatefulWidget {
  @override
  _SecondClassState createState() => _SecondClassState();
}

class _SecondClassState extends State<SecondClass> {
  int counter = 0;

  //Increases counter by 1
  void _increaseCounter() {
    setState(() {
      counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("MyApp"),
        centerTitle: true,
      ),
      body: Column(
        children: <Widget>[
          FirstClass(counter: counter, increaseCounter: _increaseCounter), //Displays the button to increase 'counter'
          FlatButton(
              child: Text("Submit"),
              onPressed: () {
                print(counter.toString()); //I need to get the value of 'counter' here to use elsewhere
              }),
        ],
      ),
    );
  }
}

class FirstClass extends StatefulWidget {
  final int counter;
  final Function increaseCounter;

  FirstClass({this.counter, this.increaseCounter});

  final _FirstClassState firstClassState = _FirstClassState();

  @override
  _FirstClassState createState() => firstClassState;
}

class _FirstClassState extends State<FirstClass> {
  @override
  Widget build(BuildContext context) {
    //A button which increases counter when clicked
    return FlatButton.icon(
      icon: Icon(Icons.add),
      label: Text("Counter: ${widget.counter}"),
      onPressed: () {
        widget.increaseCounter();
      },
    );
  }
}

从另一个类中颤振地访问StatefulWidget的State类变量

1 个答案: