Flutter 在更改控制器的文本时将文本字段光标设置为启动答案

【问题标题】：Flutter sets textfield cursor to start when changing controller's textFlutter 在更改控制器的文本时将文本字段光标设置为启动
【发布时间】：2021-04-10 21:33:56
【问题描述】：

我有一个可重用的文本字段类，如下所示：

import 'package:flutter/material.dart';

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

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      home: MyHomePage(),
    );
  }
}

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

class _MyHomePageState extends State<MyHomePage> {
  String value = "";

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        child: Center(
          child: MyTextField(
            value: value,
            onChange: (val) {
              setState(() {
                value = val;
              });
            },
          ),
        ),
      ),
    );
  }
}

typedef ChangeCallback = void Function(String value);

class MyTextField extends StatefulWidget {
  final ChangeCallback onChange;
  final String value;

  const MyTextField({this.onChange = _myDefaultFunc, this.value = ""});
  
  static _myDefaultFunc(String value){}

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

class _MyTextFieldState extends State<MyTextField> {
  final controller = TextEditingController();

  @override
  void initState() {
    controller.text = widget.value;
    super.initState();
  }

  @override
  void didUpdateWidget(covariant MyTextField oldWidget) {
    controller.text = widget.value;
    super.didUpdateWidget(oldWidget);
  }

  @override
  Widget build(BuildContext context) {
    return TextField(
      controller: controller,
      onChanged: (value) {
        widget.onChange(value);
      },
    );
  }
}

如您所见，如果值发生更改，则调用onChange 回调，并且该值再次发送回TextField。这个问题是每次我更新值时，TextField 总是将光标设置为开始。可能是因为更新的值每次都被发送回TextField？不确定。你能帮我解决这个问题吗？

【问题讨论】：

标签： flutter dart

【解决方案1】：

不要使用onChanged 方法来获取文本字段的值，而是传递一个TextEditingController。

class MyTextField extends StatefulWidget {
  final TextEditingController controller;
  final String defaultValue;

  const MyTextField({@required this.controller, this.defaultValue = ''});

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

class _MyTextFieldState extends State<MyTextField> {
  @override
  void initState() {
    widget.controller.text = widget.defaultValue;
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return TextField(
      controller: widget.controller,
    );
  }
}

这样，您可以在父小部件中声明 TextEditingController 以获取值，就像您通常使用 Flutter 的原生 TextFormField 一样。

【讨论】：

【解决方案2】：

无需更新 didUpdateWidget 中的值

//@override
//   void didUpdateWidget(covariant MyTextField oldWidget) {
//     controller.text = widget.value;
//     super.didUpdateWidget(oldWidget);
//   }

我刚刚注释掉了这个函数，代码工作正常以下是完整代码

import 'package:flutter/material.dart';

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

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      home: MyHomePage(),
    );
  }
}

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

class _MyHomePageState extends State<MyHomePage> {
  String value = "";

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        child: Column(children: [
          SizedBox(height:50),
          Text("text input: $value"),
          SizedBox(height:50),
          Center(
            child: MyTextField(
              value: value,
              onChange: (val) {
                setState(() {
                  value = val;
                });
              },
            ),
          ),
        ]),
      ),
    );
  }
}

typedef ChangeCallback = void Function(String value);

class MyTextField extends StatefulWidget {
  final ChangeCallback onChange;
  final String value;

  const MyTextField({this.onChange = _myDefaultFunc, this.value = ""});

  static _myDefaultFunc(String value) {}

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

class _MyTextFieldState extends State<MyTextField> {
  final controller = TextEditingController();

  @override
  void initState() {
    controller.text = widget.value;
    super.initState();
  }

//   @override
//   void didUpdateWidget(covariant MyTextField oldWidget) {
//     controller.text = widget.value;
//     super.didUpdateWidget(oldWidget);
//   }

  @override
  Widget build(BuildContext context) {
    return TextField(
      controller: controller,
      onChanged: (value) {
        widget.onChange(value);
      },
    );
  }
}

【讨论】：