如何在 flutter 中使用进度指示器？

Question

我是 flutter 的新手，想知道在我的布局中添加CircularProgressIndicator更好方法。 例如，我的登录视图。 这个视图有用户名、密码和登录按钮。 我确实想创建一个覆盖布局（使用Opacity ），在加载时显示进度指示器，就像我在 NativeScript 中使用的那样，但我对如何做以及是否是更好的方法感到困惑。 例如，在 NativeScript 上，我在主布局中添加 IndicatorActivity 并将 busy 设置为 true 或 false，以便在加载时覆盖所有视图组件。

编辑：

我能够达到这个结果：

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  bool _loading = false;

  void _onLoading() {
    setState(() {
      _loading = true;
      new Future.delayed(new Duration(seconds: 3), _login);
    });
  }


  Future _login() async{
    setState((){
      _loading = false;
    });
  }

  @override
  Widget build(BuildContext context) {


      var body = new Column(
          children: <Widget>[
            new Container(
              height: 40.0,
              padding: const EdgeInsets.all(10.0),
              margin: const EdgeInsets.fromLTRB(15.0, 150.0, 15.0, 0.0),
              decoration: new BoxDecoration(
                color: Colors.white,
              ),
              child: new TextField(
                decoration: new InputDecoration.collapsed(hintText: "username"),
              ),
            ),
            new Container(
              height: 40.0,
              padding: const EdgeInsets.all(10.0),
              margin: const EdgeInsets.all(15.0),
              decoration: new BoxDecoration(
                color: Colors.white,
              ),
              child: new TextField(
                decoration: new InputDecoration.collapsed(hintText: "password"),
              ),
            ),
          ],
        );


      var bodyProgress = new Container(
        child: new Stack(
          children: <Widget>[
            body,
            new Container(
              alignment: AlignmentDirectional.center,
              decoration: new BoxDecoration(
                color: Colors.white70,
              ),
              child: new Container(
                decoration: new BoxDecoration(
                  color: Colors.blue[200],
                  borderRadius: new BorderRadius.circular(10.0)
                ),
                width: 300.0,
                height: 200.0,
                alignment: AlignmentDirectional.center,
                child: new Column(
                  crossAxisAlignment: CrossAxisAlignment.center,
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: <Widget>[
                    new Center(
                      child: new SizedBox(
                        height: 50.0,
                        width: 50.0,
                        child: new CircularProgressIndicator(
                          value: null,
                          strokeWidth: 7.0,
                        ),
                      ),
                    ),
                    new Container(
                      margin: const EdgeInsets.only(top: 25.0),
                      child: new Center(
                        child: new Text(
                          "loading.. wait...",
                          style: new TextStyle(
                            color: Colors.white
                          ),
                        ),
                      ),
                    ),
                  ],
                ),
              ),
            ),
          ],
        ),
      );

      return new Scaffold(
        appBar: new AppBar(
          title: new Text(widget.title),
        ),
        body: new Container(
          decoration: new BoxDecoration(
            color: Colors.blue[200]
          ),
          child: _loading ? bodyProgress : body
        ),
        floatingActionButton: new FloatingActionButton(
          onPressed: _onLoading,
          tooltip: 'Loading',
          child: new Icon(Icons.check),
        ),
      );
  }
}

我仍在适应状态的想法。 使用 flutter 时，此代码在预期范围内吗？

Answer 1

在 Flutter 中，有几种处理异步动作的方法。

一种懒惰的方法是使用模态。 这将阻止用户输入，从而防止任何不需要的操作。 这将需要对您的代码进行很少的更改。 只需将您的_onLoading修改为以下内容：

void _onLoading() {
  showDialog(
    context: context,
    barrierDismissible: false,
    builder: (BuildContext context) {
      return Dialog(
        child: new Row(
          mainAxisSize: MainAxisSize.min,
          children: [
            new CircularProgressIndicator(),
            new Text("Loading"),
          ],
        ),
      );
    },
  );
  new Future.delayed(new Duration(seconds: 3), () {
    Navigator.pop(context); //pop dialog
    _login();
  });
}

最理想的方法是使用FutureBuilder和有状态的小部件。 这是你开始的。 诀窍是，您可以直接使用Future<MyUser> user ，而不是在您的状态下使用boolean loading = false

然后将它作为参数传递给FutureBuilder ，它会在完成时为您提供一些信息，例如“hasData”或MyUser的实例。

这将导致这样的事情：

@immutable
class MyUser {
  final String name;

  MyUser(this.name);
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      home: new MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  Future<MyUser> user;

  void _logIn() {
    setState(() {
      user = new Future.delayed(const Duration(seconds: 3), () {
        return new MyUser("Toto");
      });
    });
  }

  Widget _buildForm(AsyncSnapshot<MyUser> snapshot) {
    var floatBtn = new RaisedButton(
      onPressed:
          snapshot.connectionState == ConnectionState.none ? _logIn : null,
      child: new Icon(Icons.save),
    );
    var action =
        snapshot.connectionState != ConnectionState.none && !snapshot.hasData
            ? new Stack(
                alignment: FractionalOffset.center,
                children: <Widget>[
                  floatBtn,
                  new CircularProgressIndicator(
                    backgroundColor: Colors.red,
                  ),
                ],
              )
            : floatBtn;

    return new ListView(
      padding: const EdgeInsets.all(15.0),
        children: <Widget>[
          new ListTile(
            title: new TextField(),
          ),
          new ListTile(
            title: new TextField(obscureText: true),
          ),
          new Center(child: action)
        ],
    );
  }

  @override
  Widget build(BuildContext context) {
    return new FutureBuilder(
      future: user,
      builder: (context, AsyncSnapshot<MyUser> snapshot) {
        if (snapshot.hasData) {
          return new Scaffold(
            appBar: new AppBar(
              title: new Text("Hello ${snapshot.data.name}"),
            ),
          );
        } else {
          return new Scaffold(
            appBar: new AppBar(
              title: new Text("Connection"),
            ),
            body: _buildForm(snapshot),
          );
        }
      },
    );
  }
}

Answer 2

对我来说，一种巧妙的方法是在登录过程发生时在底部显示一个SnackBar ，这是我的意思的一个例子：

这是设置SnackBar的方法。

为您的Scaffold定义一个全局键

final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();

将其添加到您的Scaffold key属性

return new Scaffold(
      key: _scaffoldKey,
.......

我的登录按钮onPressed回调：

onPressed: () {
                  _scaffoldKey.currentState.showSnackBar(
                      new SnackBar(duration: new Duration(seconds: 4), content:
                      new Row(
                        children: <Widget>[
                          new CircularProgressIndicator(),
                          new Text("  Signing-In...")
                        ],
                      ),
                      ));
                  _handleSignIn()
                      .whenComplete(() =>
                      Navigator.of(context).pushNamed("/Home")
                  );
                }

这实际上取决于您要如何构建布局，我不确定您的想法。

编辑

您可能希望这样，我使用了 Stack 来实现此结果，并且仅基于onPressed显示或隐藏我的指标

class TestSignInView extends StatefulWidget {
  @override
  _TestSignInViewState createState() => new _TestSignInViewState();
}


class _TestSignInViewState extends State<TestSignInView> {
  bool _load = false;
  @override
  Widget build(BuildContext context) {
    Widget loadingIndicator =_load? new Container(
      color: Colors.grey[300],
      width: 70.0,
      height: 70.0,
      child: new Padding(padding: const EdgeInsets.all(5.0),child: new Center(child: new CircularProgressIndicator())),
    ):new Container();
    return new Scaffold(
      backgroundColor: Colors.white,
      body:  new Stack(children: <Widget>[new Padding(
        padding: const EdgeInsets.symmetric(vertical: 50.0, horizontal: 20.0),
        child: new ListView(

          children: <Widget>[
            new Column(
              mainAxisAlignment: MainAxisAlignment.center,
              crossAxisAlignment: CrossAxisAlignment.center
              ,children: <Widget>[
            new TextField(),
            new TextField(),

            new FlatButton(color:Colors.blue,child: new Text('Sign In'),
                onPressed: () {
              setState((){
                _load=true;
              });

                  //Navigator.of(context).push(new MaterialPageRoute(builder: (_)=>new HomeTest()));
                }
            ),

            ],),],
        ),),
        new Align(child: loadingIndicator,alignment: FractionalOffset.center,),

      ],));
  }

}

Answer 3

创建一个 bool isLoading并将其设置为false 。 在三元运算符的帮助下，当用户单击登录按钮时，将isLoading的状态设置为true 。 您将获得圆形加载指示器代替登录按钮

 isLoading ? new PrimaryButton(
                      key: new Key('login'),
                      text: 'Login',
                      height: 44.0,
                      onPressed: setState((){isLoading = true;}))
                  : Center(
                      child: CircularProgressIndicator(),
                    ),

您可以在单击登录之前查看屏幕截图

点击登录后

同时，您可以运行登录过程和登录用户。 如果用户凭据错误，那么您将再次将setState的isLoading为false ，这样加载指示器将变得不可见，并且登录按钮对用户可见。 顺便说一句，代码中使用的primaryButton是我的自定义按钮。 您可以对button中的OnPressed执行相同操作。

Answer 4

1.无插件

    class IndiSampleState extends State<ProgHudPage> {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
        appBar: new AppBar(
          title: new Text('Demo'),
        ),
        body: Center(
          child: RaisedButton(
            color: Colors.blueAccent,
            child: Text('Login'),
            onPressed: () async {
              showDialog(
                  context: context,
                  builder: (BuildContext context) {
                    return Center(child: CircularProgressIndicator(),);
                  });
              await loginAction();
              Navigator.pop(context);
            },
          ),
        ));
  }

  Future<bool> loginAction() async {
    //replace the below line of code with your login request
    await new Future.delayed(const Duration(seconds: 2));
    return true;
  }
}

2.带插件

检查这个插件progress_hud

在 pubspec.yaml 文件中添加依赖项

dev_dependencies:
  progress_hud: 

导入包

import 'package:progress_hud/progress_hud.dart';

下面给出了示例代码来显示和隐藏指标

class ProgHudPage extends StatefulWidget {
  @override
  _ProgHudPageState createState() => _ProgHudPageState();
}

class _ProgHudPageState extends State<ProgHudPage> {
  ProgressHUD _progressHUD;
  @override
  void initState() {
    _progressHUD = new ProgressHUD(
      backgroundColor: Colors.black12,
      color: Colors.white,
      containerColor: Colors.blue,
      borderRadius: 5.0,
      loading: false,
      text: 'Loading...',
    );
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
        appBar: new AppBar(
          title: new Text('ProgressHUD Demo'),
        ),
        body: new Stack(
          children: <Widget>[
            _progressHUD,
            new Positioned(
                child: RaisedButton(
                  color: Colors.blueAccent,
                  child: Text('Login'),
                  onPressed: () async{
                    _progressHUD.state.show();
                    await loginAction();
                    _progressHUD.state.dismiss();
                  },
                ),
                bottom: 30.0,
                right: 10.0)
          ],
        ));
  }

  Future<bool> loginAction()async{
    //replace the below line of code with your login request
    await new Future.delayed(const Duration(seconds: 2));
    return true;
  }
}

Answer 5

第 1 步：创建对话框

   showAlertDialog(BuildContext context){
      AlertDialog alert=AlertDialog(
        content: new Row(
            children: [
               CircularProgressIndicator(),
               Container(margin: EdgeInsets.only(left: 5),child:Text("Loading" )),
            ],),
      );
      showDialog(barrierDismissible: false,
        context:context,
        builder:(BuildContext context){
          return alert;
        },
      );
    }

第 2 步：调用它

showAlertDialog(context);
await firebaseAuth.signInWithEmailAndPassword(email: email, password: password);
Navigator.pop(context);

带有对话框和登录表单的示例

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:firebase_auth/firebase_auth.dart';
class DynamicLayout extends StatefulWidget{
  @override
  State<StatefulWidget> createState() {
    // TODO: implement createState
    return new MyWidget();
    }
  }
showAlertDialog(BuildContext context){
  AlertDialog alert=AlertDialog(
    content: new Row(
        children: [
           CircularProgressIndicator(),
           Container(margin: EdgeInsets.only(left: 5),child:Text("Loading" )),
        ],),
  );
  showDialog(barrierDismissible: false,
    context:context,
    builder:(BuildContext context){
      return alert;
    },
  );
}

  class MyWidget extends State<DynamicLayout>{
  Color color = Colors.indigoAccent;
  String title='app';
  GlobalKey<FormState> globalKey=GlobalKey<FormState>();
  String email,password;
  login() async{
   var currentState= globalKey.currentState;
   if(currentState.validate()){
        currentState.save();
        FirebaseAuth firebaseAuth=FirebaseAuth.instance;
        try {
          showAlertDialog(context);
          AuthResult authResult=await firebaseAuth.signInWithEmailAndPassword(
              email: email, password: password);
          FirebaseUser user=authResult.user;
          Navigator.pop(context);
        }catch(e){
          print(e);
        }
   }else{

   }
  }
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
        appBar:AppBar(
        title: Text("$title"),
        ) ,
          body: Container(child: Form(
            key: globalKey,
            child: Container(
              padding: EdgeInsets.all(10),
              child: Column(children: <Widget>[
              TextFormField(decoration: InputDecoration(icon: Icon(Icons.email),labelText: 'Email'),
              // ignore: missing_return
              validator:(val){
                if(val.isEmpty)
                  return 'Please Enter Your Email';
              },
              onSaved:(val){
                email=val;
              },
              ),
                TextFormField(decoration: InputDecoration(icon: Icon(Icons.lock),labelText: 'Password'),
             obscureText: true,
                  // ignore: missing_return
                  validator:(val){
                    if(val.isEmpty)
                      return 'Please Enter Your Password';
                  },
                  onSaved:(val){
                    password=val;
                  },
              ),
                RaisedButton(color: Colors.lightBlue,textColor: Colors.white,child: Text('Login'),
                  onPressed:login),
            ],)
              ,),)
         ),
    );
  }
}

Answer 6

我采用了以下方法，它使用了一个简单的模态进度指示器小部件，该小部件包装了您想要在异步调用期间创建模态的任何内容。

包中的示例还解决了如何在进行异步调用以验证表单时处理表单验证（有关此问题的详细信息，请参阅flutter/issues/9688 ）。 例如，无需离开表单，此异步表单验证方法可用于在注册时根据数据库中的现有名称验证新用户名。

https://pub.dartlang.org/packages/modal_progress_hud

这是随包提供的示例的演示（带有源代码）：

示例可以适应其他模态进度指示器行为（如不同的动画、模态中的附加文本等）。

Answer 7

我建议使用这个插件flutter_easyloading

flutter_easyloading 是 Fl​​utter App 的干净轻量级加载小部件，易于使用，无需上下文，支持 iOS 和 Android

将此添加到您的包的pubspec.yaml文件中：

dependencies:
  flutter_easyloading: ^2.0.0

现在在您的 Dart 代码中，您可以使用：

import 'package:flutter_easyloading/flutter_easyloading.dart';

要使用首先，在MaterialApp / CupertinoApp初始化FlutterEasyLoading

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter EasyLoading',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter EasyLoading'),
      builder: EasyLoading.init(),
    );
  }
}

EasyLoading 是一个单例，因此您可以在任何地方自定义加载样式，如下所示：

import 'dart:async';
import 'package:flutter/material.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter_easyloading/flutter_easyloading.dart';
import './custom_animation.dart';

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

void configLoading() {
  EasyLoading.instance
    ..displayDuration = const Duration(milliseconds: 2000)
    ..indicatorType = EasyLoadingIndicatorType.fadingCircle
    ..loadingStyle = EasyLoadingStyle.dark
    ..indicatorSize = 45.0
    ..radius = 10.0
    ..progressColor = Colors.yellow
    ..backgroundColor = Colors.green
    ..indicatorColor = Colors.yellow
    ..textColor = Colors.yellow
    ..maskColor = Colors.blue.withOpacity(0.5)
    ..userInteractions = true
    ..customAnimation = CustomAnimation();
}

然后，根据您的要求使用

import 'package:flutter/material.dart';
import 'package:flutter_easyloading/flutter_easyloading.dart';
import 'package:dio/dio.dart';

class TestPage extends StatefulWidget {
  @override
  _TestPageState createState() => _TestPageState();
}

class _TestPageState extends State<TestPage> {
  @override
  void initState() {
    super.initState();
    // EasyLoading.show();
  }

  @override
  void deactivate() {
    EasyLoading.dismiss();
    super.deactivate();
  }

  void loadData() async {
    try {
      EasyLoading.show();
      Response response = await Dio().get('https://github.com');
      print(response);
      EasyLoading.dismiss();
    } catch (e) {
      EasyLoading.showError(e.toString());
      print(e);
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Flutter EasyLoading'),
      ),
      body: Center(
        child: FlatButton(
          textColor: Colors.blue,
          child: Text('loadData'),
          onPressed: () {
            loadData();
            // await Future.delayed(Duration(seconds: 2));
            // EasyLoading.show(status: 'loading...');
            // await Future.delayed(Duration(seconds: 5));
            // EasyLoading.dismiss();
          },
        ),
      ),
    );
  }
}

Answer 8

这是我的堆栈解决方案

import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'dart:async';

final themeColor = new Color(0xfff5a623);
final primaryColor = new Color(0xff203152);
final greyColor = new Color(0xffaeaeae);
final greyColor2 = new Color(0xffE8E8E8);

class LoadindScreen extends StatefulWidget {
  LoadindScreen({Key key, this.title}) : super(key: key);
  final String title;
  @override
  LoginScreenState createState() => new LoginScreenState();
}

class LoginScreenState extends State<LoadindScreen> {
  SharedPreferences prefs;

  bool isLoading = false;

  Future<Null> handleSignIn() async {
    setState(() {
      isLoading = true;
    });
    prefs = await SharedPreferences.getInstance();
    var isLoadingFuture = Future.delayed(const Duration(seconds: 3), () {
      return false;
    });
    isLoadingFuture.then((response) {
      setState(() {
        isLoading = response;
      });
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text(
            widget.title,
            style: TextStyle(color: primaryColor, fontWeight: FontWeight.bold),
          ),
          centerTitle: true,
        ),
        body: Stack(
          children: <Widget>[
            Center(
              child: FlatButton(
                  onPressed: handleSignIn,
                  child: Text(
                    'SIGN IN WITH GOOGLE',
                    style: TextStyle(fontSize: 16.0),
                  ),
                  color: Color(0xffdd4b39),
                  highlightColor: Color(0xffff7f7f),
                  splashColor: Colors.transparent,
                  textColor: Colors.white,
                  padding: EdgeInsets.fromLTRB(30.0, 15.0, 30.0, 15.0)),
            ),

            // Loading
            Positioned(
              child: isLoading
                  ? Container(
                      child: Center(
                        child: CircularProgressIndicator(
                          valueColor: AlwaysStoppedAnimation<Color>(themeColor),
                        ),
                      ),
                      color: Colors.white.withOpacity(0.8),
                    )
                  : Container(),
            ),
          ],
        ));
  }
}

Answer 9

您可以为中心透明进度指示器执行此操作

Future<Null> _submitDialog(BuildContext context) async {
  return await showDialog<Null>(
      context: context,
      barrierDismissible: false,
      builder: (BuildContext context) {
        return SimpleDialog(
          elevation: 0.0,
          backgroundColor: Colors.transparent,
          children: <Widget>[
            Center(
              child: CircularProgressIndicator(),
            )
          ],
        );
      });
}

Answer 10

{
isloading? progressIos:Container()

progressIos(int i) {
    return Container(
        color: i == 1
            ? AppColors.liteBlack
            : i == 2 ? AppColors.darkBlack : i == 3 ? AppColors.pinkBtn : '',
        child: Center(child: CupertinoActivityIndicator()));
  }
}

Answer 11

您可以改用 FutureBuilder 小部件。 这需要一个必须是 Future 的参数。 然后你可以使用一个快照，它是登录时异步调用当时的状态，一旦它结束，异步函数返回的状态将被更新，未来的构建器将重建自己，这样你就可以请求新的状态。

FutureBuilder(
  future:  myFutureFunction(),
  builder: (context, AsyncSnapshot<List<item>> snapshot) {
    if (!snapshot.hasData) {
      return Center(
        child: CircularProgressIndicator(),
      );
    } else {
     //Send the user to the next page.
  },
);

这里有一个关于如何构建未来的例子

Future<void> myFutureFunction() async{
 await callToApi();}

Answer 12

以屏幕为中心：

Column(
    mainAxisAlignment: MainAxisAlignment.center,
    mainAxisSize: MainAxisSize.max,
    crossAxisAlignment: CrossAxisAlignment.start,
    children: [
        Row(
            mainAxisAlignment: MainAxisAlignment.center,
            mainAxisSize: MainAxisSize.max,
            children: [CircularProgressIndicator()])
      ])

Answer 13

class Loader extends StatefulWidget {
      @override
      State createState() => LoaderState();
    }

    class LoaderState extends State<Loader> with SingleTickerProviderStateMixin {
      AnimationController controller;
      Animation<double> animation;

      @override
      void initState() {
        super.initState();
        controller = AnimationController(
            duration: Duration(milliseconds: 1200), vsync: this);
        animation = CurvedAnimation(parent: controller, curve: Curves.elasticOut);
        animation.addListener(() {
          this.setState(() {});
        });
        animation.addStatusListener((AnimationStatus status) {});
        controller.repeat();
      }

      @override
      void dispose() {
        controller.dispose();
        super.dispose();
      }

      @override
      Widget build(BuildContext context) {
        return Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Container(
              color: Colors.blue,
              height: 3.0,
              width: animation.value * 100.0,
            ),
            Padding(
              padding: EdgeInsets.only(bottom: 5.0),
            ),
            Container(
              color: Colors.blue[300],
              height: 3.0,
              width: animation.value * 75.0,
            ),
            Padding(
              padding: EdgeInsets.only(bottom: 5.0),
            ),
            Container(
              color: Colors.blue,
              height: 3.0,
              width: animation.value * 50.0,
            )
          ],
        );
      }
    }


    Expanded(
                        child: Padding(
                          padding:
                              EdgeInsets.only(left: 20.0, right: 5.0, top:20.0),
                          child: GestureDetector(
                            onTap: () {
                              Navigator.push(
                                  context,
                                  MaterialPageRoute(
                                      builder: (context) => FirstScreen()));
                            },
                            child: Container(
                                alignment: Alignment.center,
                                height: 45.0,
                                decoration: BoxDecoration(
                                    color: Color(0xFF1976D2),
                                    borderRadius: BorderRadius.circular(9.0)),
                                child: Text('Login',
                                    style: TextStyle(
                                        fontSize: 20.0, color: Colors.white))),
                          ),
                        ),
                      ),

Answer 14

对于您的情况，也许可以通过使用带有圆形指示器的模式来完成。 但我建议使用一个简单的插件https://pub.dev/packages/flutter_easyloading 。

• 安装超级简单。 只需在终端中运行这个flutter pub add flutter_easyloading
• 把它放在你的 main.dart 应用程序中

import 'package:flutter/material.dart';
import 'package:kunjungi_dokter/pages/welcome.dart';
import 'package:flutter_easyloading/flutter_easyloading.dart';  // <- add this

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

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: const Welcome(),
      builder: EasyLoading.init(), // <- add this
    );
  }
}

• 为了显示模式或加载小部件，在我的例子中，我在登录屏幕的 mya _login 函数中显示它：

import 'package:flutter_easyloading/flutter_easyloading.dart';

// ... other code

_login() async {
    EasyLoading.show(status: 'loading...', maskType: EasyLoadingMaskType.black); // code to show modal with masking
    var data = await LoginAPI.connectToAPI(
        emailController.text, passwordController.text);
    if (data.isError) {
      EasyLoading.showError('Login Error: ' + data.message); // code to show modal without masking and auto close
    } else {
      await storage.write(key: 'token', value: data.token);
      await storage.write(key: 'email', value: emailController.text);
      EasyLoading.showSuccess('Login Success!'); // code to show modal without masking and auto close
      Navigator.of(context)
          .push(MaterialPageRoute(builder: ((context) => const Home())));
    }
  }
// ... other code

• 提示，您可以使用它来关闭模态：

EasyLoading.dismiss();

Answer 15

你需要一个图书馆

void onLoading() {
     showDialog(
      context: context,
       barrierDismissible: false,
       builder: (BuildContext context) {
          return GFLoader(
          type: GFLoaderType.android,        
         );
        },
    );
  }

然后在代码中需要的地方使用这个 function

onLoading;

Answer 16

 //Start loadding
    Future<void> loader() async {
            return await showDialog<void>(
              context: context,
              barrierDismissible: false,
              builder: (BuildContext context) {
                return const SimpleDialog(
                  elevation: 0.0,
                  backgroundColor: Colors.transparent,
                  // can change this to your prefered color
                  children: <Widget>[
                    Center(
                      child: CircularProgressIndicator(),
                    )
                  ],
                );
              },
            );
          }

    //Stop loadding
    Navigator.of(context).pop();