我想知道,你如何在Dart中将调用转换回 Future(Promise)。这是如何:

Dart — 将回调转换为 Future

Dart — convert callback to Future

Future time(int time) async {

  Completer c = new Completer();
  new Timer(new Duration(seconds: time), (){
    c.complete('done with time out');
  });

  return c.future;
}

If you have any other questions let me know! I try to respond within the hour!

https://gitee.com/bigpowers/f-lutter_im_yin/blob/master/lib/webSocketPage/chatContact.dart

json.decode() Unexpected end of input (at character 1)

import 'dart:convert';

import 'package:flutter/material.dart';
import 'package:restaurant_app/globalVar.dart';
import 'package:restaurant_app/homescreen.dart';
 import 'package:flutter_secure_storage/flutter_secure_storage.dart';
 import 'package:restaurant_app/signup.dart';
import 'package:http/http.dart' as http;
import 'package:flutter_html_view/html_parser.dart';

class SignIn extends StatefulWidget {
 @override
_SignInState createState() => _SignInState();
}

class _SignInState extends State<SignIn> with SingleTickerProviderStateMixin 
{
TabController controller;
TextEditingController _email = new TextEditingController();
TextEditingController _password = new TextEditingController();
bool loading;

 final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState> 
();

@override
void initState() {
// TODO: implement initState
super.initState();
controller = new TabController(length: 2, vsync: this);
loading = false;
_email = new TextEditingController(text: "rajeshvishnani");
_password = new TextEditingController(text: "Rajesh@MaaKiRasoi");
}

@override
void dispose() {
// TODO: implement dispose
super.dispose();
controller.dispose();
setState(() {
  loading = false;
});
_email.dispose();
_password.dispose();
}

final GlobalKey<FormState> _formKey = GlobalKey<FormState>();
bool _autoValidate = false;

Future _writer(String username, String password, String token) async {
final storage = new FlutterSecureStorage();
await storage.write(key: authTokenKeys, value: token);
print(await storage.read(key: authTokenKeys));
await storage.write(key: nameKeys, value: username);
print(await storage.read(key: nameKeys));
await storage.write(key: passwordKeys, value: password);
}

  static final String authTokenKeys = 'auth_token';
static final String nameKeys = 'username';
static final String passwordKeys = 'password';

_login(username, password) async {
setState(() {
  loading = true;
});

var body = json.encode({
  "username": username,
  "password": password,
});

Map<String, String> headers = {
  'Content-type': 'application/json',
  'Accept': 'application/json',
};

await http
    .post("${GlobalVar.Ip}/wp-json/jwt-auth/v1/token",
        body: body, headers: headers)
    .then((response) {
  var body = json.decode(response.body);

  if (response.statusCode == 200) {
    // TODO: you need to store body['token'] to use in some authentication
    loading = false;
    _writer(_email.text, _password.text, body['token']);
    Navigator.pushReplacement(context,
        MaterialPageRoute(builder: (BuildContext ctx) => HomePage()));
  } else {
    // TODO: alert message
    final snackBar = SnackBar(
      content: Text(body['message']),
    );
    _scaffoldKey.currentState.showSnackBar(snackBar);
  }
  setState(() {
    loading = false;
  });
  });
}

@override
 Widget build(BuildContext context) {
return Scaffold(
  key: _scaffoldKey,
  resizeToAvoidBottomPadding: false,
  body: Container(
    decoration: BoxDecoration(
      image: DecorationImage(
        image: AssetImage('images/art.png'),
        fit: BoxFit.fill,
        colorFilter: ColorFilter.mode(
            Colors.white12.withOpacity(0.2), BlendMode.dstATop),
      ),
    ),
    child: ListView(
      shrinkWrap: true,
      physics: BouncingScrollPhysics(),
      children: <Widget>[
        SizedBox(
          height: MediaQuery.of(context).size.height / 30,
        ),
        Align(
          alignment: Alignment.topCenter,
          child: CircleAvatar(
            backgroundColor: Colors.grey,
            radius: 55.0,
            backgroundImage: AssetImage('images/logo.png'),
          ),
        ),
        SizedBox(
          height: MediaQuery.of(context).size.height / 30,
        ),
        Stack(
          alignment: Alignment.center,
          children: <Widget>[
            SizedBox(
              height: MediaQuery.of(context).size.height / 300,
              child: new Center(
                child: new Container(
                  height: 10.0,
                  color: Colors.black12,
                ),
              ),
            ),
            Row(
              children: <Widget>[
                SizedBox(
                  width: MediaQuery.of(context).size.width / 4,
                ),
                Chip(
                  label: Text(
                    "SIGN IN",
                    style: TextStyle(color: Colors.white, fontSize: 18.0),
                  ),
                  backgroundColor: Color(0xFFD1A155),
                ),
                SizedBox(
                  width: MediaQuery.of(context).size.width / 35,
                  child: Container(
                    width: MediaQuery.of(context).size.height / 12,
                    height: 2.0,
                    color: Colors.white,
                  ),
                ),
                Chip(
                  label: Text(
                    "SIGN UP",
                    style: TextStyle(color: Colors.white, fontSize: 18.0),
                  ),
                  backgroundColor: Colors.black87,
                ),
              ],
            )
          ],
        ),
        SizedBox(
          height: MediaQuery.of(context).size.height / 35,
        ),
        Align(
            alignment: Alignment.center,
            child: Text(
              "Welcome back!",
              style: TextStyle(
                fontSize: 20.0,
                color: Color(0xFFD1A155),
              ),
            )),
        SizedBox(
          height: MediaQuery.of(context).size.height / 30,
        ),
        Form(
          key: _formKey,
          autovalidate: _autoValidate,
          child: Column(
            children: <Widget>[
              Theme(
                data: ThemeData(
                  hintColor: Colors.black26,
                  primaryColor: Color(0xFFD1A155),
                ),
                child: Padding(
                  padding: const EdgeInsets.only(left: 15.0, right: 15.0),
                  child: TextFormField(
                    keyboardType: TextInputType.emailAddress,
                    //validator: _email.text.isEmpty?:null,
                    controller: _email,

                    decoration: InputDecoration(
                        border:
                            OutlineInputBorder(borderSide: BorderSide()),
                        prefixIcon: Icon(
                          Icons.email,
                          color: Color(0xFFD1A155),
                        ),
                        hintText: 'Email Address',
                        hintStyle: TextStyle(
                            color: Colors.black,
                            fontWeight: FontWeight.w400)),
                  ),
                ),
              ),
              SizedBox(
                height: MediaQuery.of(context).size.height / 45,
              ),
              Theme(
                data: ThemeData(
                    primaryColor: Color(0xFFD1A155),
                    hintColor: Colors.black26),
                child: Padding(
                  padding: const EdgeInsets.only(left: 15.0, right: 15.0),
                  child: TextFormField(
                    keyboardType: TextInputType.text,
                    obscureText: true,
                    controller: _password,
                  decoration: InputDecoration(
                        border:
                            OutlineInputBorder(borderSide: BorderSide()),
                        prefixIcon: Icon(
                          Icons.lock,
                          color: Color(0xFFD1A155),
                        ),
                        hintText: 'Password',
                        hintStyle: TextStyle(
                            color: Colors.black,
                            fontWeight: FontWeight.w400)),
                  ),
                ),
              ),
              Padding(
                padding: const EdgeInsets.only(right: 15.0, left: 10.0),
                child: Row(
                  mainAxisAlignment: MainAxisAlignment.spaceBetween,
                  children: <Widget>[
                    Row(
                      children: <Widget>[
                        ActionChip(
                          onPressed: () {},
                          avatar: Checkbox(
                            value: false,
                            onChanged: (bool z) {
                              print(z);
                            },
                            activeColor: Color(0xFFD1A155),
                          ),
                          label: Text("Remember Me"),
                          backgroundColor: Colors.transparent,
                        ),
                      ],
                    ),
                    Text(
                      "Forgot Password?",
                      style: TextStyle(
                        color: Color(0xFFD1A155),
                      ),
                    ),
                  ],
                ),
              ),
              Padding(
                padding: const EdgeInsets.only(left: 15.0, right: 15.0),
                child: InkWell(
                  onTap: () {
                    _login(_email.text, _password.text);
         //                        Navigator.push(
        //                            context,
    //                            MaterialPageRoute(
     //                                builder: (context) => HomePage()));
                  },
                  child: loading
                      ? CircularProgressIndicator()
                      : Container(
                          height: MediaQuery.of(context).size.height / 13,
                          //width: MediaQuery.of(context).size.height / 1.8,
                          decoration: BoxDecoration(
                            color: Color(0xFFD1A155),
                            borderRadius: BorderRadius.circular(5.0),
                          ),
                          child: Center(
                            child: Text(
                              "LOGIN",
                              style: TextStyle(
                                  color: Colors.white, fontSize: 18.0),
                            ),
                          ),
                        ),
                ),
              )
            ],
          ),
        ),
        SizedBox(
          height: MediaQuery.of(context).size.height / 15,
        ),
        Stack(
          alignment: Alignment.center,
          children: <Widget>[
            SizedBox(
              height: 2.0,
              child: new Center(
                child: new Container(
                  height: 10.0,
                  color: Colors.black12,
                ),
              ),
            ),
            Container(
              height: MediaQuery.of(context).size.height / 18,
              width: MediaQuery.of(context).size.height / 11,
              decoration: BoxDecoration(
                  borderRadius: BorderRadius.circular(23.0),
                  color: Colors.white,
                  border: Border.all(color: Colors.black12)),
              child: Center(
                  child: Text(
                "OR",
                style: TextStyle(fontSize: 18.0),
              )),
            ),
          ],
        ),
        SizedBox(
          height: MediaQuery.of(context).size.height / 30,
        ),
        Padding(
          padding: const EdgeInsets.only(left: 15.0, right: 15.0),
          child: Row(
            children: <Widget>[
              Container(
                height: MediaQuery.of(context).size.height / 13,
                width: MediaQuery.of(context).size.width / 2.2,
                decoration: BoxDecoration(
                    borderRadius: BorderRadius.circular(5.0),
                    color: Colors.white,
                    border: Border.all(color: Colors.black12)),
                child: Row(
                  children: <Widget>[
                    SizedBox(
                      width: 18.0,
                    ),
                    Icon(Icons.tag_faces),
                    SizedBox(
                      width: 10.0,
                    ),
                    Text(
                      "Facebook",
                      style: TextStyle(fontSize: 22.0, color: Colors.blue),
                    ),
                  ],
                ),
              ),
              SizedBox(
                width: MediaQuery.of(context).size.width / 40,
              ),
              Container(
                height: MediaQuery.of(context).size.height / 13,
                width: MediaQuery.of(context).size.width / 2.3,
                decoration: BoxDecoration(
                    borderRadius: BorderRadius.circular(5.0),
                    color: Colors.white,
                    border: Border.all(color: Colors.black12)),
                child: Row(
                  children: <Widget>[
                    SizedBox(
                      width: 18.0,
                    ),
                    Icon(Icons.tag_faces),
                    SizedBox(
                      width: 10.0,
                    ),
                    Text(
                      "Google+",
                      style: TextStyle(fontSize: 22.0, color: Colors.red),
                    ),
                  ],
                ),
              ),
            ],
          ),
        ),
        SizedBox(
          height: MediaQuery.of(context).size.height / 20,
        ),
        Align(
          alignment: Alignment.center,
          child: InkWell(
            onTap: () => Navigator.push(
                context, MaterialPageRoute(builder: (context) => SignUp())),
            child: RichText(
                text: TextSpan(
                    text: "Don't have an account?",
                    style: TextStyle(fontSize: 20.0, color: Colors.black87),
                    children: <TextSpan>[
                  TextSpan(
                      text: ' Sign up',
                      style: TextStyle(
                          color: Color(0xFFD1A155),
                          fontWeight: FontWeight.bold)),
                ])),
          ),
        ),
        SizedBox(
          height: MediaQuery.of(context).size.height / 30,
        ),
      ],
    ),
  ),
  );
 }
}

遇到类似这样的的错误,请确保.decode方法的参数不应该是空对象。而不是使用这一行:

var body = json.decode(response.body);

试试这个,希望它对你有用。

if(response.body.isNotEmpty) {
    json.decode(response.body);
}

image-20210824163611592

推荐个神器,压缩png图片,https://tinify.cn/

https://juejin.cn/post/6859185139402932238 InteractiveViewer

image-20210824163913854