如何解决此 For 循环不工作错误？ for 循环在 Flutter 中只工作一次

Question

如何解决这个 For loop not working 错误？ for 循环在 Flutter 中只工作一次

这是一个简单的登录表单。如果用户名和密码匹配转到用户 其他页面转到管理页面。

方法代码：

checkLogin(){
  setState(() {
  for(var c=0;c < global.user_name_arr.length-1 ; c++){
   if(global.user_name_arr[c]==myController.text&&global.user_password_arr[c]==myControllerPwd.text)

        Navigator.push(context, MaterialPageRoute(builder: (context)=>user()),);
      else
        Navigator.push(context, MaterialPageRoute(builder:(context)=>admin()),);   }    
 }); }

RaiseButton 代码：

new RaisedButton(
                  child:new Text("Click"),
                  onPressed:checkLogin, 
                )

global.dart

library user_login.globlas;

var user_name_arr=['bhanuka','isuru','sampath'];
var user_password_arr=['1234','123','12'];

Answer 1

首先，让我们重构您的代码 :) 像这样创建一个用户类：

class User {
  final String name;
  final String password;

  User(this.name, this.password); 
}

接下来，修复您的全局用户集合：

final validUsers = [User('bhanuka', '1234'), User('isuru', '123'), User('sampath', '12')];

现在，使用此代码执行正确的导航：

checkLogin() {
  if (validUsers.indexWhere((user) => user.name == myController.text && user.password == myControllerPwd.text) >= 0) {
    Navigator.push(context, MaterialPageRoute(builder: (context)=>user()),);
  } else {
    Navigator.push(context, MaterialPageRoute(builder:(context)=>admin()),);   
  }         
}

有更好的方法来进行这种比较，但我想这对于您的用例来说已经足够了。

Answer 2

这里你使用 if else 来判断条件是对还是错，其中一个部分被执行。

   import 'package:flutter/material.dart';

void main() => runApp(new MaterialApp(
      title: 'Forms in Flutter',
      home: new LoginPage(),
    ));

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

class _LoginData {
  String email = '';
  String password = '';
}

class _LoginPageState extends State<LoginPage> {
  final GlobalKey<FormState> _formKey = new GlobalKey<FormState>();
  _LoginData _data = new _LoginData();
  var user_name_arr = ['bhanuka', 'isuru', 'sampath'];
  var user_password_arr = ['1234', '123', '12'];
  var p;
  void submit() {
    if (this._formKey.currentState.validate()) {
      _formKey.currentState.save(); // Save our form now.
      if (user_name_arr.contains(_data.email)) {
        p = user_name_arr.indexOf(_data.email);
        if (user_password_arr.elementAt(p) == _data.password) {
          Navigator.push(context, MaterialPageRoute(builder: (context)=>user()),);
        } else {
          Navigator.push(
            context,
            MaterialPageRoute(builder: (context) => admin()),
          );
        }
      } else {
        Navigator.push(
          context,
          MaterialPageRoute(builder: (context) => admin()),
        );
      }
    }
  }

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

    return new Scaffold(
      appBar: new AppBar(
        title: new Text('Login'),
      ),
      body: new Container(
          padding: new EdgeInsets.all(20.0),
          child: new Form(
            key: this._formKey,
            child: new ListView(
              children: <Widget>[
                new TextFormField(
                    keyboardType: TextInputType
                        .emailAddress, // Use email input type for emails.
                    decoration: new InputDecoration(
                        hintText: 'you@example.com',
                        labelText: 'E-mail Address'),
                    onSaved: (String value) {
                      this._data.email = value;
                    }),
                new TextFormField(
                    obscureText: true, // Use secure text for passwords.
                    decoration: new InputDecoration(
                        hintText: 'Password', labelText: 'Enter your password'),
                    onSaved: (String value) {
                      this._data.password = value;
                    }),
                new Container(
                  width: screenSize.width,
                  child: new RaisedButton(
                    child: new Text(
                      'Login',
                      style: new TextStyle(color: Colors.white),
                    ),
                    onPressed: this.submit,
                    color: Colors.blue,
                  ),
                  margin: new EdgeInsets.only(top: 20.0),
                )
              ],
            ),
          )),
    );
  }
}

class user extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        child: Center(child: new Text("user")),
      ),
    );
  }
}

class admin extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        child: Center(child: new Text("admin")),
      ),
    );
  }
}