flutter - 在等待 API 响应时显示加载指示器

Question

所以我有一个注册页面并且注册功能运行良好。
现在我所需要的只是按下“注册”按钮后的加载指示器。
我已经混合了所有我能想到的关键词在谷歌中搜索，我已经尝试了所有但没有任何效果。

以下是我尝试过的事情:

使用 FutureBuilder :

RaisedButton(
                    onPressed: () async {
                      FutureBuilder<http.Response>(
                        future: registerUser(),
                        builder: (context, snapshot) {
                          if (snapshot.hasData) {
                            return Text("SUCCESS");
                          }
                          if (snapshot.hasError) {
                            return Text("ERROR");
                          }
                          return new Center(
                              child: new CircularProgressIndicator());
                        },
                      );
                    },
                    color: Color(colorPrimary),
                    shape: RoundedRectangleBorder(
                        borderRadius: new BorderRadius.circular(30.0)),
                    child: Text("SignUp"),
                  )

在这个方法中，方法被调用，但指标没有显示

使用图书馆 progress_hud :
这个我认为是有效的，但即使我把它放在 Center 中小部件，
它仍然会到达屏幕底部，显示 overlapping with pixels错误。

还有其他更好的解决方案吗？或者我应该找到一种方法来解决这个重叠的错误？

谢谢你的帮助!

Answer 1

请使用包 modal_progress_hud https://pub.dev/packages/modal_progress_hud
ModalProgressHUD 必须作为第一个 child 在脚手架主体下
我的工作代码片段

 @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: ModalProgressHUD(
        inAsyncCall: _isLoading,
        child: SingleChildScrollView(
          child: Container(
               ...

完整示例代码

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:modal_progress_hud/modal_progress_hud.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: LoginPage(
        onSignIn: () => print('login successful!'),
      ),
    );
  }
}

class LoginPage extends StatefulWidget {
  final VoidCallback _onSignIn;

  LoginPage({@required onSignIn})
      : assert(onSignIn != null),
        _onSignIn = onSignIn;

  @override
  _LoginPageState createState() => _LoginPageState();
}

class _LoginPageState extends State<LoginPage> {
  // maintains validators and state of form fields
  final GlobalKey<FormState> _loginFormKey = GlobalKey<FormState>();

  // manage state of modal progress HUD widget
  bool _isInAsyncCall = false;

  bool _isInvalidAsyncUser = false; // managed after response from server
  bool _isInvalidAsyncPass = false; // managed after response from server

  String _username;
  String _password;
  bool _isLoggedIn = false;

  // validate user name
  String _validateUserName(String userName) {
    if (userName.length < 8) {
      return 'Username must be at least 8 characters';
    }

    if (_isInvalidAsyncUser) {
      // disable message until after next async call
      _isInvalidAsyncUser = false;
      return 'Incorrect user name';
    }

    return null;
  }

  // validate password
  String _validatePassword(String password) {
    if (password.length < 8) {
      return 'Password must be at least 8 characters';
    }

    if (_isInvalidAsyncPass) {
      // disable message until after next async call
      _isInvalidAsyncPass = false;
      return 'Incorrect password';
    }

    return null;
  }

  void _submit() {
    if (_loginFormKey.currentState.validate()) {
      _loginFormKey.currentState.save();

      // dismiss keyboard during async call
      FocusScope.of(context).requestFocus(new FocusNode());

      // start the modal progress HUD
      setState(() {
        _isInAsyncCall = true;
      });

      // Simulate a service call
      Future.delayed(Duration(seconds: 1), () {
        final _accountUsername = 'username1';
        final _accountPassword = 'password1';
        setState(() {
          if (_username == _accountUsername) {
            _isInvalidAsyncUser = false;
            if (_password == _accountPassword) {
              // username and password are correct
              _isInvalidAsyncPass = false;
              _isLoggedIn = true;
            } else
              // username is correct, but password is incorrect
              _isInvalidAsyncPass = true;
          } else {
            // incorrect username and have not checked password result
            _isInvalidAsyncUser = true;
            // no such user, so no need to trigger async password validator
            _isInvalidAsyncPass = false;
          }
          // stop the modal progress HUD
          _isInAsyncCall = false;
        });
        if (_isLoggedIn)
          // do something
          widget._onSignIn();
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Modal Progress HUD Demo'),
        backgroundColor: Colors.blue,
      ),
      // display modal progress HUD (heads-up display, or indicator)
      // when in async call
      body: ModalProgressHUD(
        child: SingleChildScrollView(
          child: Container(
            padding: const EdgeInsets.all(16.0),
            child: buildLoginForm(context),
          ),
        ),
        inAsyncCall: _isInAsyncCall,
        // demo of some additional parameters
        opacity: 0.5,
        progressIndicator: CircularProgressIndicator(),
      ),
    );
  }

  Widget buildLoginForm(BuildContext context) {
    final TextTheme textTheme = Theme.of(context).textTheme;
    // run the validators on reload to process async results
    _loginFormKey.currentState?.validate();
    return Form(
      key: this._loginFormKey,
      child: Column(
        children: [
          Padding(
            padding: const EdgeInsets.all(8.0),
            child: TextFormField(
              key: Key('username'),
              decoration: InputDecoration(
                  hintText: 'enter username', labelText: 'User Name'),
              style: TextStyle(fontSize: 20.0, color: textTheme.button.color),
              validator: _validateUserName,
              onSaved: (value) => _username = value,
            ),
          ),
          Padding(
            padding: const EdgeInsets.all(8.0),
            child: TextFormField(
              key: Key('password'),
              obscureText: true,
              decoration: InputDecoration(
                  hintText: 'enter password', labelText: 'Password'),
              style: TextStyle(fontSize: 20.0, color: textTheme.button.color),
              validator: _validatePassword,
              onSaved: (value) => _password = value,
            ),
          ),
          Padding(
            padding: const EdgeInsets.all(32.0),
            child: RaisedButton(
              onPressed: _submit,
              child: Text('Login'),
            ),
          ),
          Padding(
            padding: const EdgeInsets.all(8.0),
            child: _isLoggedIn
                ? Text(
              'Login successful!',
              key: Key('loggedIn'),
              style: TextStyle(fontSize: 20.0),
            )
                : Text(
              'Not logged in',
              key: Key('notLoggedIn'),
              style: TextStyle(fontSize: 20.0),
            ),
          ),
        ],
      ),
    );
  }
}