如何从另一个 dart 文件中调用有状态小部件（有表单）方法？- Flutter
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【中文标题】如何从另一个 dart 文件中调用有状态小部件（有表单）方法？- Flutter【英文标题】：How to Call stateful widget(have form) method from another dart file?- Flutter 【发布时间】：2020-01-03 09:23:20 【问题描述】：我在有状态小部件中有一个表单，在我的有状态小部件中，我使用提交方法验证我的表单。
在我的应用程序中，我在另一个 dart 文件的另一个页面中显示该表单。
我的表单在新页面和 appbar 操作中可见，我正在调用提交方法，但我不知道如何在新 dart 文件中调用该提交方法。
【问题讨论】：
【参考方案1】：我认为你的问题不是验证逻辑，你可以在回调中做到这一点 我认为您的情况是单击提交按钮时您可能会使用 SnackBar。您使用 SnackBar 来显示错误，并且您不想在 appbar 中重复此逻辑。
诀窍是使用 GlobalKey 来保持 YourFormState 并使用 key.currentState 在 YourFormState 中调用函数，因此提交按钮和 appbar 动作可以调用相同的函数
final key = new GlobalKey<MyCustomFormState>();
...
appBar: AppBar(
title: Text(widget.title),
actions: <Widget>[
// action button
IconButton(
icon: Icon(Icons.access_alarm),
onPressed: ()
key.currentState.validateform();
,
),
]),
...
children: <Widget>[
MyCustomForm(key: key),
...
class MyCustomForm extends StatefulWidget
MyCustomForm( Key key ) : super(key: key);
完整的工作代码
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
final key = new GlobalKey<MyCustomFormState>();
class MyApp extends StatelessWidget
// This widget is the root of your application.
@override
Widget build(BuildContext context)
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
// This is the theme of your application.
//
// Try running your application with "flutter run". You'll see the
// application has a blue toolbar. Then, without quitting the app, try
// changing the primarySwatch below to Colors.green and then invoke
// "hot reload" (press "r" in the console where you ran "flutter run",
// or simply save your changes to "hot reload" in a Flutter IDE).
// Notice that the counter didn't reset back to zero; the application
// is not restarted.
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
class MyHomePage extends StatefulWidget
MyHomePage(Key key, this.title) : super(key: key);
// This widget is the home page of your application. It is stateful, meaning
// that it has a State object (defined below) that contains fields that affect
// how it looks.
// This class is the configuration for the state. It holds the values (in this
// case the title) provided by the parent (in this case the App widget) and
// used by the build method of the State. Fields in a Widget subclass are
// always marked "final".
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
var myCustomForm = MyCustomForm();
class _MyHomePageState extends State<MyHomePage>
int _counter = 0;
void _incrementCounter()
setState(()
// This call to setState tells the Flutter framework that something has
// changed in this State, which causes it to rerun the build method below
// so that the display can reflect the updated values. If we changed
// _counter without calling setState(), then the build method would not be
// called again, and so nothing would appear to happen.
_counter++;
);
@override
Widget build(BuildContext context)
// This method is rerun every time setState is called, for instance as done
// by the _incrementCounter method above.
//
// The Flutter framework has been optimized to make rerunning build methods
// fast, so that you can just rebuild anything that needs updating rather
// than having to individually change instances of widgets.
return Scaffold(
appBar: AppBar(
// Here we take the value from the MyHomePage object that was created by
// the App.build method, and use it to set our appbar title.
title: Text(widget.title),
actions: <Widget>[
// action button
IconButton(
icon: Icon(Icons.access_alarm),
onPressed: ()
key.currentState.validateform();
,
),
]),
body: Center(
// Center is a layout widget. It takes a single child and positions it
// in the middle of the parent.
child: Column(
// Column is also layout widget. It takes a list of children and
// arranges them vertically. By default, it sizes itself to fit its
// children horizontally, and tries to be as tall as its parent.
//
// Invoke "debug painting" (press "p" in the console, choose the
// "Toggle Debug Paint" action from the Flutter Inspector in android
// Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
// to see the wireframe for each widget.
//
// Column has various properties to control how it sizes itself and
// how it positions its children. Here we use mainAxisAlignment to
// center the children vertically; the main axis here is the vertical
// axis because Columns are vertical (the cross axis would be
// horizontal).
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
MyCustomForm(key: key),
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.display1,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
), // This trailing comma makes auto-formatting nicer for build methods.
);
class MyCustomForm extends StatefulWidget
MyCustomForm( Key key ) : super(key: key);
@override
MyCustomFormState createState()
return MyCustomFormState();
// Create a corresponding State class.
// This class holds data related to the form.
class MyCustomFormState extends State<MyCustomForm>
// Create a global key that uniquely identifies the Form widget
// and allows validation of the form.
//
// Note: This is a GlobalKey<FormState>,
// not a GlobalKey<MyCustomFormState>.
final _formKey = GlobalKey<FormState>();
@override
Widget build(BuildContext context)
// Build a Form widget using the _formKey created above.
return Form(
key: _formKey,
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
TextFormField(
validator: (value)
if (value.isEmpty)
return 'Please enter some text';
return null;
,
),
Padding(
padding: const EdgeInsets.symmetric(vertical: 16.0),
child: RaisedButton(
onPressed: ()
// Validate returns true if the form is valid, or false
// otherwise.
validateform();
,
child: Text('Submit'),
),
),
],
),
);
void validateform()
// Validate returns true if the form is valid, or false
// otherwise.
if (_formKey.currentState.validate())
// If the form is valid, display a Snackbar.
Scaffold.of(context)
.showSnackBar(SnackBar(content: Text('Processing Data')));
演示与 SnackBar 配合使用
【讨论】：
谢谢兄弟，您的代码运行良好。我有2个疑问。在 MyCustomFormState 类中，您删除了 _（下划线）。第一个疑问）。删除下划线会导致应用性能出现问题吗？第二个疑问）。我们已经为 FormState 使用了 GlobalKey，现在为 MyCustomFormState 创建了另一个 GlobalKey，因此使用 2 GlobalKey 将产生任何问题。我不太了解 GlobalKey。我是 Flutter 的初学者。请解释 MyCustomFormState 是来自谷歌的官方示例。我没有修改它。下划线表示私有。没有性能问题。两个不同的变量（键）没有冲突。 详情可以看这个。 ***.com/questions/46542768/… 哦，谢谢兄弟。而且我不需要 Snackbar。我在 1 个飞镖文件中有表格。在主 dart 文件中，我正在显示我的表单。在 Appbar 中，我正在调用提交按钮，它位于另一个 dart 文件中。因此，在调用该函数时，它的验证器使用 null 调用。这是我的问题。现在它解决了。 嗨，我试过了，但它显示以下错误 ════════ 手势捕获的异常═══════════════════ ═════════════════════════════════════════════以下无方法抛出错误处理手势：在 null 上调用了方法“test”。接收者：null 尝试调用：test()【参考方案2】：您可以在另一个小部件的顶部创建 VoidCallback final，这将触发父小部件的操作。
class FormWidget extends StatefulWidget
@override
_FormWidgetState createState() => _FormWidgetState();
class _FormWidgetState extends State<FormWidget>
@override
Widget build(BuildContext context)
return Column(
children: <Widget>[
//here goes your form and everything else
SubmitButton(
onClick: ()
//perform the actions you need
,
),
],
);
class SubmitButton extends StatelessWidget
final VoidCallback onClick;
const SubmitButton(Key key, this.onClick) : super(key: key);
@override
Widget build(BuildContext context)
return GestureDetector(
onTap: onClick,
child:Container(
//your button
),
);
【讨论】：
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