如何在颤动中从另一个类访问一个类方法？

Question

大家好，我是新来的飞镖

我做了图片上传功能

但我在制作过程中遇到了麻烦。

class pictureBox() 无法识别 getImage() ,,

这是我的全部代码：

class writeprofile extends StatefulWidget {
  @override
  _writeprofileState createState() => _writeprofileState();
}

class _writeprofileState extends State<writeprofile> {
  File _image;


  @override
  Widget build(BuildContext context) {
    Future getImage() async{
      var image= await ImagePicker.pickImage(source: ImageSource.gallery);
      setState(() {
        _image = image;
        print('Image Path $_image');
      });
    }

    Future uploadPic(BuildContext context) async{
      String filName = basename(_image.path);
      StorageReference firebaseStorageRef = FirebaseStorage.instance.ref().child(filName);
      StorageUploadTask uploadTask = firebaseStorageRef.putFile(_image);
      StorageTaskSnapshot taskSnapshot = await uploadTask.onComplete;
      setState(() {
        print("Profile pic upload !!");
        Scaffold.of(context).showSnackBar(SnackBar(content: Text('Profile pic Upload !!')));
      });
    }


    return Scaffold(
      body: Builder(
        builder: (context)=> Center(
          child: Container(
            child: Container(
              child: Column(
                children: <Widget>[
                  Padding(
                    padding: EdgeInsets.only(top: 70),
                    child: Text(
                      '사진 선택',
                      style: TextStyle(
                        fontSize: 30,
                        fontWeight: FontWeight.w500,
                      ),
                    ),
                  ),
                  Padding(
                    padding: EdgeInsets.only(top: 10, bottom: 50),
                    child: Container(
                      height: 1,
                      width: MediaQuery.of(context).size.width / 1.4,
                      color: Colors.black26,
                    ),
                  ),
                  Container(
                    width: MediaQuery.of(context).size.width / 1.5,
                    height: MediaQuery.of(context).size.height / 15,
                    alignment: FractionalOffset.center,
                    decoration: BoxDecoration(
                      color: const Color.fromRGBO(250, 80, 120, 1),
                      borderRadius: BorderRadius.all(const Radius.circular(30)),
                    ),
                    child: Text(
                      "가이드 라인을 읽어주세요 !",
                      style: TextStyle(
                        color: Colors.white,
                        fontSize: 20,
                        fontWeight: FontWeight.w300,
                        letterSpacing: 0.3,
                      ),
                    ),
                  ),
                  Padding(
                    padding: const EdgeInsets.only(top: 100),
                    child: Row(
                      children: <Widget>[
                        PictureBox(),
                        PictureBox(),
                        PictureBox(),
                      ],
                    ),
                  ),
                  Padding(
                    padding: const EdgeInsets.only(top: 10),
                    child: Row(
                      children: <Widget>[
                        PictureBox(),
                        PictureBox(),
                        PictureBox(),
                      ],
                    ),
                  ),
                  InkWell(
                    onTap: (){uploadPic(context);},
                    child: Padding(
                      padding: EdgeInsets.only(top: 50),
                      child: Container(
                        width: MediaQuery.of(context).size.width / 3,
                        height: MediaQuery.of(context).size.height /20,
                        alignment: FractionalOffset.center,
                        decoration: BoxDecoration(
                          color: const Color.fromRGBO(250, 80, 100, 1),
                          borderRadius: BorderRadius.all(const Radius.circular(30)),
                        ),
                        child: Text(
                          "Next",
                          style: TextStyle(
                            color: Colors.white,
                            fontSize: 20,
                            fontWeight: FontWeight.w500,
                            letterSpacing: 0.3,
                          ),
                        ),
                      ),
                    ),
                  ),
                ],
              ),
            ),
          ),
        ),
      ),
    );
  }
}

class PictureBox extends StatefulWidget {
  @override
  _PictureBoxState createState() => _PictureBoxState();
}

class _PictureBoxState extends State<PictureBox>{
  @override
  Widget build(BuildContext context) {
    return Container(
      child: InkWell(
        onTap: (){getImage(context);},
        child: Padding(
          padding: EdgeInsets.only(left: 10),
          child:Container(
            width: MediaQuery.of(context).size.width / 3.3,
            height: MediaQuery.of(context).size.height / 7,
            color: Colors.black12,
            child: Center(
              child: (_image!=null)? Image.file(_image, fit:BoxFit.fill)
                  :Icon(
                Icons.camera_alt,
                color: Colors.black26,
              ),
            ),
          ),
        ),
      ),
    );
  }
}

这是我的代码，我想在 PictureBox 中使用“Future getImage()” 如何在 PictureBox 中运行 getImage()？

另外如何解决 PictureBox 中的错误 'undefined name '_image'' ？

Answer 1

_ 表示私有变量。所以删除_ 并尝试。

Answer 2

如果你想在 StatefulWidget 小部件中调用函数
您需要使用 GlobalKey 来保留 YourFormState 并使用 key.currentState 在 YourFormState 中调用函数
下面的demo是appbar action调用表单StatefulWidget里面的一个函数，所以appbar action和表单提交按钮可以使用相同的函数，snackbar也可以正常工作

代码sn-p

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')));
    }
  }
}

Answer 3

@Killer Whale，如果你想从 parent 调用 child 方法并在 child 中调用 setState()，那么你可以使用 GlobalKey。

GlobalKey<WriteprofileState> globalKey =new GlobalKey<WriteprofileState>();

_writeprofileState远程私有标识符，写为WriteprofileState。

然后将全局密钥从父级传递给WriteprofileState

喜欢：

Widget build(BuildContext conext){
return Container(
child: Writeprofile(
key:globalKey
)
);
}

然后将此密钥传递给超类，Writeprofile(Key key):super(key:key); 现在从父类你可以访问所有子类的方法。

globalKey.currentState.methodName();