Flutter设置文本字段光标在更改控制器文本时启动

debugcn 发表于 Dev

达蒙

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，如果更改了值，则会onChange调用callback并将该值再次发送回TextField。问题是每次我更新值时，TextField总是将光标设置为开始。可能是因为更新后的值TextField每次都发送回去了吗？不确定。你能帮我吗？

哈韦迪沙克

无需更新didUpdateWidget中的值

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

我刚刚注释掉了此功能，下面的代码工作正常，是完整的代码

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);
      },
    );
  }
}

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