Flutter 将文本字段光标设置为在更改控制器文本时启动

Question

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);
},
);
}
}

正如您所看到的，如果值发生了更改，则会调用onChange回调，并且该值会再次发送回TextField。这样做的问题是，每次更新值时，TextField都会将光标设置为起点。可能是因为每次都会将更新后的值发送回TextField？不确定。你能帮我做这个吗？

Answer 1

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，代码运行良好下面是完整的代码

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);
},
);
}
}

Answer 2

不使用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,
);
}
}

通过这种方式，您可以在父窗口小部件中声明一个TextEditingController来获得值，就像通常使用Flutter的原生TextFormField一样。