对null调用了getter“keys”

Question

我还不了解框架，你能帮我解决这个错误吗？我正在尝试获取基本用户数据并在此处输入图像描述

颤振医生:

[！]Android工具链-为Android设备开发（Android SDK版本30.0.0）！某些Android许可证不被接受。要解决此问题，请运行：flutter博士--android-许可证[！]Android Studio（4.0版）X Flutter插件未安装；这增加了Flutter特定功能。X Dart插件未安装；这增加了Dart特定功能。[√]连接的设备（1个可用）

!医生在2类中发现了问题。

import 'package:dio/dio.dart';
import 'package:flutter/material.dart';
import 'constants.dart';
import 'package:simple_auth/simple_auth.dart' as simpleAuth;
import 'package:simple_auth_flutter/simple_auth_flutter.dart';


class Inst_Login extends StatefulWidget {
  Inst_Login({Key key}) : super(key: key);

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

class _Inst_LoginState extends State<Inst_Login> {
  String _errorMsg;
  Map _userData;

  final simpleAuth.InstagramApi _igApi = simpleAuth.InstagramApi(
    "instagram",
    Constants.igClientId,
    Constants.igClientSecret,
    Constants.igRedirectURL,
    scopes: [
      'user_profile', // For getting username, account type, etc.
      'user_media', // For accessing media count & data like posts, videos etc.
    ],
  );

  @override
  void initState() {
    super.initState();
    SimpleAuthFlutter.init(context);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Instagram Basic Display API Demo'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Visibility(
              visible: _userData != null,
              child: Text(
                _userData.keys.fold(
                    '', (kvText, key) => kvText + "$key: ${_userData[key]} \n"),
                textAlign: TextAlign.center,
              ),
              replacement:
              Text("Click the button below to get Instagram Login."),
            ),
            FlatButton.icon(
              icon: Icon(Icons.input),
              label: Text(
                "Get Profile Data",
              ),
              onPressed: _loginAndGetData,
              color: Colors.pink.shade400,
            ),
            if (_errorMsg != null) Text("Error occured: $_errorMsg"),
          ],
        ),
      ),
    );
  }

  Future<void> _loginAndGetData() async {
    _igApi.authenticate().then(
          (simpleAuth.Account _user) async {
        simpleAuth.OAuthAccount user = _user;

        var igUserResponse =
        await Dio(BaseOptions(baseUrl: 'https://graph.instagram.com')).get(
          '/me',
          queryParameters: {
            // Get the fields you need.
            // https://developers.facebook.com/docs/instagram-basic-display-api/reference/user
            "fields": "username,id,account_type,media_count",
            "access_token": user.token,
          },
        );

        setState(() {
          _userData = igUserResponse.data;
          _errorMsg = null;
        });
      },
    ).catchError(
          (Object e) {
        setState(() => _errorMsg = e.toString());
      },
    );
  }
}

Answer 1

即使您使用的是< code>Visibility widget，该widget也不应该有null _userdata。如果您执行的api调用是< code >异步的并返回< code>Future，那么请使用< code>FutureBuilder

未来生成器的代码将是 -

import 'package:dio/dio.dart';
import 'package:flutter/material.dart';
import 'constants.dart';
import 'package:simple_auth/simple_auth.dart' as simpleAuth;
import 'package:simple_auth_flutter/simple_auth_flutter.dart';

class Inst_Login extends StatefulWidget {
  Inst_Login({Key key}) : super(key: key);

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

class _Inst_LoginState extends State<Inst_Login> {
  String _errorMsg;
  Map _userData;

  final simpleAuth.InstagramApi _igApi = simpleAuth.InstagramApi(
    "instagram",
    Constants.igClientId,
    Constants.igClientSecret,
    Constants.igRedirectURL,
    scopes: [
      'user_profile', // For getting username, account type, etc.
      'user_media', // For accessing media count & data like posts, videos etc.
    ],
  );

  @override
  void initState() {
    super.initState();
    SimpleAuthFlutter.init(context);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Instagram Basic Display API Demo'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            FutureBuilder(
              future: _loginAndGetData(),
              builder: (context, snapshot) {
                if (snapshot.connectionState == ConnectionState.done)
                  return Text(
                    _userData.keys.fold('',
                        (kvText, key) => kvText + "$key: ${_userData[key]} \n"),
                    textAlign: TextAlign.center,
                  );
                return Text("Click the button below to get Instagram Login.");
              },
            ),
            FlatButton.icon(
              icon: Icon(Icons.input),
              label: Text(
                "Get Profile Data",
              ),
              onPressed: _loginAndGetData,
              color: Colors.pink.shade400,
            ),
            if (_errorMsg != null) Text("Error occured: $_errorMsg"),
          ],
        ),
      ),
    );
  }

  Future<void> _loginAndGetData() async {
    _igApi.authenticate().then(
      (simpleAuth.Account _user) async {
        simpleAuth.OAuthAccount user = _user;

        var igUserResponse =
            await Dio(BaseOptions(baseUrl: 'https://graph.instagram.com')).get(
          '/me',
          queryParameters: {
            // Get the fields you need.
            // https://developers.facebook.com/docs/instagram-basic-display-api/reference/user
            "fields": "username,id,account_type,media_count",
            "access_token": user.token,
          },
        );

        setState(() {
          _userData = igUserResponse.data;
          _errorMsg = null;
        });
      },
    ).catchError(
      (Object e) {
        setState(() => _errorMsg = e.toString());
      },
    );
  }
}

如果你在评论中有任何问题或疑问，希望这能帮助你。