• 我正在尝试使用flutter和nodejs制作一个具有简单登录/注册功能的应用程序。
• 在Postman中，它可以发送请求
• 我在Chrome上运行它，它工作完美，但不能在Android Emmulator（和物理设备）中工作。

然后“我发现我必须和当地的主持人做些改变”，但是不知道是什么...
可能是个很初级的问题
main.dart

import 'package:frontend/signin.dart';

void main() {
  runApp(MaterialApp(
    debugShowCheckedModeBanner: false,
    home: Signin(),
  ));
}

signin.dart

import 'package:flutter/material.dart';
import 'package:flutter_svg/svg.dart';
import 'package:frontend/dashboard.dart';
import 'package:frontend/signup.dart';
import 'package:frontend/user.dart';
import 'package:google_fonts/google_fonts.dart';
import 'package:http/http.dart' as http;

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

  @override
  State<Signin> createState() => _SigninState();
}

class _SigninState extends State<Signin> {
  final _formKey = GlobalKey<FormState>();
  Future save() async {
    var res = await http.post(
      "http://localhost:8080/signin",
      // "http://10.0.2.2/signin",
      headers: <String, String>{
        "Context-Type": 'application.json;charSet=UTF-8'
      },
      body: <String, String>{
        'email': user.email,
        'password': user.password,
      },
    );
    print(res.body);
    Navigator.push(
      context,
      new MaterialPageRoute(builder: (context) => Dashboard()),
    );
  }

  User user = User('', '');
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SingleChildScrollView(
        child: Stack(
          
          children: [
            Positioned(
                top: 0,
                child: SvgPicture.asset(
                  'images/top.svg',
                  width: 400,
                  height: 150,
                )),
            Container(
              alignment: Alignment.center,
              child: Form(
                key: _formKey,
                child: Column(
                  crossAxisAlignment: CrossAxisAlignment.center,
                  mainAxisAlignment: MainAxisAlignment.start,
                  children: [
                    const SizedBox(
                      height: 150,
                    ),
                    Text(
                      'Signin',
                      style: GoogleFonts.pacifico(
                        fontWeight: FontWeight.bold,
                        fontSize: 50,
                        color: Colors.blue,
                      ),
                    ),
                    const SizedBox(
                      height: 25,
                    ),
                    Padding(
                      padding: const EdgeInsets.all(16.0),
                      child: TextFormField(
                        controller: TextEditingController(text: user.email),
                        onChanged: (value) {
                          user.email = value;
                        },
                        validator: (value) {
                          if (value!.isEmpty) {
                            return 'Enter Something';
                          } else if (RegExp(
                                  r"^[a-zA-Z0-9.a-zA-Z0-9.!#$%&'*+-/=?^_`{|}~]+@[a-zA-Z0-9]+\.[a-zA-Z]+")
                              .hasMatch(value)) {
                            return null;
                          } else {
                            return 'Enter Valid Email';
                          }
                        },
                        decoration: InputDecoration(
                          hintText: "Enter Email",
                          enabledBorder: OutlineInputBorder(
                            borderRadius: BorderRadius.circular(50),
                            borderSide: const BorderSide(color: Colors.blue),
                          ),
                          focusedBorder: OutlineInputBorder(
                            borderRadius: BorderRadius.circular(50),
                            borderSide: const BorderSide(color: Colors.blue),
                          ),
                          errorBorder: OutlineInputBorder(
                            borderRadius: BorderRadius.circular(50),
                            borderSide: const BorderSide(color: Colors.red),
                          ),
                          focusedErrorBorder: OutlineInputBorder(
                            borderRadius: BorderRadius.circular(50),
                            borderSide: const BorderSide(color: Colors.red),
                          ),
                        ),
                      ),
                    ),
                    Padding(
                      padding: const EdgeInsets.all(16.0),
                      child: TextFormField(
                        controller: TextEditingController(text: user.email),
                        onChanged: (value) {
                          user.email = value;
                        },
                        validator: (value) {
                          if (value!.isEmpty) {
                            return 'Enter Something';
                          }
                          return null;
                        },
                        decoration: InputDecoration(
                          hintText: "Enter Password",
                          enabledBorder: OutlineInputBorder(
                            borderRadius: BorderRadius.circular(50),
                            borderSide: const BorderSide(color: Colors.blue),
                          ),
                          focusedBorder: OutlineInputBorder(
                            borderRadius: BorderRadius.circular(50),
                            borderSide: const BorderSide(color: Colors.blue),
                          ),
                          errorBorder: OutlineInputBorder(
                            borderRadius: BorderRadius.circular(50),
                            borderSide: const BorderSide(color: Colors.red),
                          ),
                          focusedErrorBorder: OutlineInputBorder(
                            borderRadius: BorderRadius.circular(50),
                            borderSide: const BorderSide(color: Colors.red),
                          ),
                        ),
                      ),
                    ),
                    Padding(
                      padding: const EdgeInsets.all(16.0),
                      child: Container(
                        height: 50,
                        width: 400,
                        child: FlatButton(
                          color: Colors.blue,
                          shape: RoundedRectangleBorder(
                              borderRadius: BorderRadius.circular(16.0)),
                          onPressed: () {
                            if (_formKey.currentState!.validate()) {
                              save();
                            } else {
                              print("NOT OK");
                            }
                          },
                          child: const Text(
                            "SIGNIN",
                            style: TextStyle(color: Colors.white),
                          ),
                        ),
                      ),
                    ),
                    Padding(
                        padding: const EdgeInsets.fromLTRB(65, 20, 0, 0),
                        child: Row(
                          children: [
                            const Text(
                              "not have account ? ",
                              style: TextStyle(
                                color: Colors.black,
                                fontWeight: FontWeight.bold,
                              ),
                            ),
                            InkWell(
                              onTap: () {
                                Navigator.push(
                                    context,
                                    new MaterialPageRoute(
                                        builder: (context) => Signup()));
                              },
                              child: const Text(
                                "Signup",
                                style: TextStyle(
                                  color: Colors.blue,
                                  fontWeight: FontWeight.bold,
                                ),
                              ),
                            ),
                          ],
                        )),
                  ],
                ),
              ),
            )
          ],
        ),
      ),
    );
  }
}

user.dart

class User {
  String email;
  String password;
  User(this.email, this.password);
}

index.js

const express = require("express");
const app = express();
const port = 8080 || process.env.PORT;
const cors = require("cors");
const bodyParser = require("body-parser");
const mongoose = require("mongoose");

mongoose.connect("mongodb://localhost:27017/mydb", {
// mongoose.connect("mongodb://10.0.2.2:27017/mydb", {
  useNewUrlParser: true,
  useUnifiedTopology: true,
});

app.use(cors());
app.use(bodyParser.urlencoded({ extended: true }));
app.use(bodyParser.json());
app.use("/", require("./routes/user.route"));

app.listen(port, () => {
  console.log("port is running on " + port);
});

谢谢你：）