当我想登录我的flutter应用程序时，我遇到了问题。当您输入您的电子邮件和密码，然后点击登录按钮，它只处理加载，但不能去到主页.在Android Studio中，出现了一个错误，就像我发送的图像一样。
this is a picture of the running error
API_service.dart

import 'package:http/http.dart' as http;
import 'dart:convert';
import '../model/login_model.dart';

class APIService {
  Future<LoginResponseModel> login(LoginRequestModel requestModel) async {
    String url = "http://192.168.100.211:8080/login";

    final response = await http.post(url, body: requestModel.toJson());
    if (response.statusCode == 200 || response.statusCode == 400) {
      return LoginResponseModel.fromJson(
        json.decode(response.body),
      );
    } else {
      throw Exception('Failed to load data!');
    }
  }
}

Login_model.dart

class LoginResponseModel {
  final String token;
  final String error;

  LoginResponseModel({this.token, this.error});

  factory LoginResponseModel.fromJson(Map<String, dynamic> json) {
    return LoginResponseModel(
      token: json["token"] != null ? json["token"] : "",
      error: json["error"] != null ? json["error"] : "",
    );
  }
}

class LoginRequestModel {
  String email;
  String password;

  LoginRequestModel({
    this.email,
    this.password,
  });

  Map<String, dynamic> toJson() {
    Map<String, dynamic> map = {
      'email': email.trim(),
      'password': password.trim(),
    };

    return map;
  }
}

登录_页面.dart

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter_crud_api_sample_app/beranda/beranda_view.dart';
import '/api/api_service.dart';
import '/model/login_model.dart';

import '../ProgressHUD.dart';

class LoginPage extends StatefulWidget {
  @override
  _LoginPageState createState() => _LoginPageState();
}

class _LoginPageState extends State<LoginPage> {
  bool hidePassword = true;
  bool isApiCallProcess = false;
  GlobalKey<FormState> globalFormKey = GlobalKey<FormState>();
  LoginRequestModel loginRequestModel;
  final scaffoldKey = GlobalKey<ScaffoldState>();
  @override
  void initState() {
    super.initState();
    loginRequestModel = new LoginRequestModel();
  }

  @override
  Widget build(BuildContext context) {
    return ProgressHUD(
      child: _uiSetup(context),
      inAsyncCall: isApiCallProcess,
      opacity: 0.3,
    );
  }

  Widget _uiSetup(BuildContext context) {
    return Scaffold(
      key: scaffoldKey,
      backgroundColor: Theme.of(context).accentColor,
      body: SingleChildScrollView(
        child: Column(
          children: <Widget>[
            Stack(
              children: <Widget>[
                Container(
                  width: double.infinity,
                  padding: EdgeInsets.symmetric(vertical: 30, horizontal: 20),
                  margin: EdgeInsets.symmetric(vertical: 85, horizontal: 20),
                  decoration: BoxDecoration(
                    borderRadius: BorderRadius.circular(20),
                    color: Theme.of(context).primaryColor,
                    boxShadow: [
                      BoxShadow(
                          color: Theme.of(context).hintColor.withOpacity(0.2),
                          offset: Offset(0, 10),
                          blurRadius: 20)
                    ],
                  ),
                  child: Form(
                    key: globalFormKey,
                    child: Column(
                      children: <Widget>[
                        SizedBox(height: 25),
                        Text(
                          "Login",
                          style: Theme.of(context).textTheme.headline2,
                        ),
                        SizedBox(height: 20),
                        new TextFormField(
                          keyboardType: TextInputType.emailAddress,
                          onSaved: (input) => loginRequestModel.email = input,
                          validator: (input) => !input.contains('@')
                              ? "Email Id should be valid"
                              : null,
                          decoration: new InputDecoration(
                            hintText: "Email Address",
                            enabledBorder: UnderlineInputBorder(
                                borderSide: BorderSide(
                                    color: Theme.of(context)
                                        .accentColor
                                        .withOpacity(0.2))),
                            focusedBorder: UnderlineInputBorder(
                                borderSide: BorderSide(
                                    color: Theme.of(context).accentColor)),
                            prefixIcon: Icon(
                              Icons.email,
                              color: Theme.of(context).accentColor,
                            ),
                          ),
                        ),
                        SizedBox(height: 20),
                        new TextFormField(
                          style:
                              TextStyle(color: Theme.of(context).accentColor),
                          keyboardType: TextInputType.text,
                          onSaved: (input) =>
                              loginRequestModel.password = input,
                          validator: (input) => input.length < 3
                              ? "Password should be more than 3 characters"
                              : null,
                          obscureText: hidePassword,
                          decoration: new InputDecoration(
                            hintText: "Password",
                            enabledBorder: UnderlineInputBorder(
                                borderSide: BorderSide(
                                    color: Theme.of(context)
                                        .accentColor
                                        .withOpacity(0.2))),
                            focusedBorder: UnderlineInputBorder(
                                borderSide: BorderSide(
                                    color: Theme.of(context).accentColor)),
                            prefixIcon: Icon(
                              Icons.lock,
                              color: Theme.of(context).accentColor,
                            ),
                            suffixIcon: IconButton(
                              onPressed: () {

                                setState(() {
                                  hidePassword = !hidePassword;
                                });
                              },
                              color: Theme.of(context)
                                  .accentColor
                                  .withOpacity(0.4),
                              icon: Icon(hidePassword
                                  ? Icons.visibility_off
                                  : Icons.visibility),
                            ),
                          ),
                        ),
                        SizedBox(height: 30),
                        FlatButton(
                          padding: EdgeInsets.symmetric(
                              vertical: 12, horizontal: 80),
                          onPressed: () {
                            if (validateAndSave()) {
                              print(loginRequestModel.toJson());

                              setState(() {
                                isApiCallProcess = true;
                              });

                              APIService apiService = new APIService();
                              apiService.login(loginRequestModel).then((value) {
                                if (value != null) {
                                  setState(() {
                                    isApiCallProcess = false;
                                  });

                                  if (value.token.isNotEmpty) {
                                    final snackBar = SnackBar(
                                        content: Text("Login Successful"));
                                    scaffoldKey.currentState
                                        .showSnackBar(snackBar);
                                  } else {
                                    final snackBar =
                                        SnackBar(content: Text(value.error));
                                    scaffoldKey.currentState
                                        .showSnackBar(snackBar);
                                  }
                                }
                              });
                            }
                          },
                          child: Text(
                            "Login",
                            style: TextStyle(color: Colors.white),
                          ),
                          color: Theme.of(context).accentColor,
                          shape: StadiumBorder(),
                        ),
                        SizedBox(height: 15),
                      ],
                    ),
                  ),
                ),
              ],
            ),
          ],
        ),
      ),
    );
  }

  bool validateAndSave() {
    final form = globalFormKey.currentState;
    if (form.validate()) {
      form.save();
      return true;
    }
    return false;
  }
}

朋友们能帮助我克服这些障碍吗？