I have declared a function in my main.dart that would help me get the deviceId. I am trying to set this to a variable of an independent class, whose constructor is later created in one of my widget.

Function:

Future<String?> _getId() async {
  var deviceInfo = DeviceInfoPlugin();
  if (Platform.isIOS) { // import 'dart:io'
    var iosDeviceInfo = await deviceInfo.iosInfo;
    return iosDeviceInfo.identifierForVendor; // Unique ID on iOS
  } else {
    var androidDeviceInfo = await deviceInfo.androidInfo;
    return androidDeviceInfo.androidId; // Unique ID on Android
  }
}

Calling it in a class as:

class _Data {
  String? fullname = '';
  String doctor = 's';
  String? deviceId = await _getId();
}

I get below error:

The await expression can only be used in an async function.

---

Complete code:

import 'dart:io';
import 'dart:async';
import 'package:flutter/material.dart';
import 'package:device_info_plus/device_info_plus.dart';

Future<String?> _getId() async {
  var deviceInfo = DeviceInfoPlugin();
  if (Platform.isIOS) { // import 'dart:io'
    var iosDeviceInfo = await deviceInfo.iosInfo;
    return iosDeviceInfo.identifierForVendor; // Unique ID on iOS
  } else {
    var androidDeviceInfo = await deviceInfo.androidInfo;
    return androidDeviceInfo.androidId; // Unique ID on Android
  }
}

void main() => runApp(const MaterialApp(
  title: 'Manager',
  home: RegisterPage(),
));


class RegisterPage extends StatefulWidget {
  const RegisterPage ({Key? key}) : super(key: key);
  @override
  State<StatefulWidget> createState() => _RegisterPageState();
}

class _Data {
  String? fullname = '';
  String doctor = 's';
  String? deviceId = await _getId();
}

class _RegisterPageState extends State<RegisterPage> {
  final GlobalKey<FormState> _formKey = GlobalKey<FormState>();
  _Data _data = _Data();

  void submit() {
      _formKey.currentState!.save();
      print('Printing the login data.');
      print('Fullname: ${_data.fullname}');
      print('Doctor: ${_data.doctor}');
      print('Device Id: ${_data.getDeviceId()}');
  }

  @override
  Widget build(BuildContext context) {
    final Size screenSize = MediaQuery.of(context).size;

    return Scaffold(
      appBar: AppBar(
        title: const Text('Manager'),
      ),
      body: Container(
          padding: const EdgeInsets.all(20.0),
          child: Form(
            key: _formKey,
            child: ListView(
              children: <Widget>[
                TextFormField(
                    keyboardType: TextInputType.text,
                    decoration: const InputDecoration(
                        hintText: 'John Doe',
                        labelText: 'Full name'
                    ),
                    onSaved: (String? value) {
                      _data.fullname = value;
                    }
                ),
                Container(
                  width: screenSize.width,
                  margin: const EdgeInsets.only(
                      top: 20.0
                  ),
                  child: ElevatedButton(
                    onPressed: submit,
                    child: const Text(
                      'Register',
                      style: TextStyle(
                          color: Colors.white
                      ),
                    ),
                  ),
                )
              ],
            ),
          )
      ),
    );
  }
}

It displays correct value for fullname on clicking submit but gives error for calling device id

CodePudding user response：

await keyword can only used with async function.

only with function, but here you called await _getId() inside a class not inside a function.

try this.

  @override
  void initState() {
    // TODO: implement initState
    super.initState();

    _getId().then((value) {
      _data.deviceId = value;
    });
    //print(_data.deviceId);
  }

CodePudding user response：

You want to initialize deviceId from the result of an asynchronous operation. Some options:

• Declare Future<String?> deviceId = _getId(); and require all callers to await it when accessing it.

• Initialize it later:

  class _Data {
    String? deviceId;
  
    _Data() {
      _getId().then((id) => deviceId = id);
    }
  }
  

  Note that with this approach, callers will not be notified when deviceId is eventually initialized.

• Make callers initialize your class asynchronously:

  class _Data {
    String? deviceId;
  
    _Data._(this.deviceId);
  
    static Future<_Data> newData() async {
      var id = await _getId();
      return _Data._(id);
    }
  }
  

Somewhat related: How to await future in global main dart of flutter?

CodePudding user response：

Many of the things you are doing would be considered bad practice. I will lay out a few changes and finally answer your question. Define your _Data class as follows:

class _Data {
  String? fullname; 
  String doctor; 
  String? deviceId; 
  _Data(this.fullname, this.doctor, this.deviceId);
}

This way your data model is not hardcoded. You may also consider making the fields final unless you have a good reason not to.

Declare the data state variable:

_Data? _data;

Define the initData method inside your state:

  Future<void> initData() async {
    var dat = _Data("fn", "doc", await _getId());
    setState(() {_data = dat; });
  }

Finally override initState:

  @override
  void initState() {
    super.initState();
    initData();
  }

Inside your build method you can pay attention to whether or not the field is null (checking if it has been initialized). There's a bunch of room for improvement here once you get it running. First you should not make the getId method top level, it would be better to have it inside a service, and you should consider using a future builder instead of having the _data state attribute nullable.