如何在 flutter 的应用程序的每个屏幕上显示名称和电子邮件

Question

我在应用程序主屏幕的抽屉中显示名称和电子邮件（从 MongoDB 获取），现在我想在我的应用程序的每个屏幕上显示该抽屉，当我点击任何页面时显示在抽屉上，那么该页面抽屉应该类似于主抽屉。

我也在传递参数，但它给我这个错误

错误：

A non-null String must be provided to a Text widget.
'package:flutter/src/widgets/text.dart':
Failed assertion: line 378 pos 10: 'data != null'

这是我的登录代码，当用户输入正确的凭据时，它将被重定向到主屏幕。


// this save() i am calling on login button 

Future save() async {

    Dio dio=new Dio();
    var data={
      'username': user.username,
      'password': user.password

    };
    await dio
    .post(localhostUrl,data: json.encode(data))
      .then((onResponse){
        print(onResponse.data['User']);
        //var name=print(onResponse.data['User']['username']);
        print(onResponse.data['User']['designation']);
        print(onResponse.data['User']['TimeIn']);
  
         //**here i am passing values to  EmployeeNavigation which is my home** 
         Navigator.push(
        context, new MaterialPageRoute(builder: (context) => EmployeeNavigation(
        name:onResponse.data['User']['username'],     
        email:onResponse.data['User']['email'],
        designation:onResponse.data['User']['designation'],
        date:onResponse.data['User']['Date'],
        timeIn:onResponse.data['User']['TimeIn'],
        timeOut:onResponse.data['User']['TimeOut'],
        )));

      }).catchError((onerror){
        print(onerror.toString());
        showAlertDialog(context);
    });
  }

这是我的 EmployeeNavigation 代码

class EmployeeNavigation extends StatefulWidget {
  var name;
  var email;
  var designation;
  var date;
  var timeIn;
  var timeOut;
  EmployeeNavigation({this.name, this.email, this.designation, this.date, this.timeIn, this.timeOut, } );
  @override
  State<StatefulWidget> createState() {
    return EmployeeNavigationState(this.name,this.email,this.designation,this.date,this.timeIn,this.timeOut);
  }
}

class EmployeeNavigationState extends State<EmployeeNavigation> {

var name;
  var email;
  var designation;
  var date;

 EmployeeNavigationState(this.name,this.email, this.designation,this.date,this.timeIn, this.timeOut );
   bool valuefirst = false;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
       title: Image.asset("assets/image/company_logo.png",height: 140,width: 280,
       ),

       backgroundColor: Colors.white,
       iconTheme: IconThemeData(color: Colors.blue,size: 20),
       //leading: new Icon(Icons.menu,color: Colors.blue,),
       actions: <Widget>[
       IconButton(
        icon: Icon(
        Icons.notifications,
        color: Colors.blue,
        size:26
      ),
     
      
    )
    ],
    ),
    drawer:new  Drawer(
      child: new ListView(
          padding: const EdgeInsets.all(0.0),
          children: <Widget>[
            new UserAccountsDrawerHeader(
                accountName: new Text(name,style: TextStyle(fontSize: 14)),  //here i am using name parameter
                accountEmail: new Text(email,style: TextStyle(fontSize: 14),),  // here i am using email parameter
                currentAccountPicture: new CircleAvatar(
                  backgroundColor:
                  Theme.of(context).platform == TargetPlatform.android
                      ? Colors.white
                      : Colors.blue,
              child: Text(
                name[0][0],
                style: TextStyle(fontSize: 40.0),
              ),
            ),
          ),
            new ListTile(
              title: new Text('Request for leave'),
              leading: Icon(Icons.request_page),
              onTap: (){
           
                Navigator.pop(context);
                  Navigator.push(context, new MaterialPageRoute(
                    builder: (context)=>new RequestForLeave(name,email)  //here i am passing name and email parameters
                    )
                  );
              },
            ),
            new ExpansionTile(
              title: new Text('History'),
              children: <Widget>[
                ListTile(
                   title:new Text("My Attendance"),
                  leading: Icon(Icons.assessment_outlined ),
                  onTap: (){
                Navigator.pop(context);
                  Navigator.push(context, new MaterialPageRoute(
                    builder: (context)=>new MyAttendance()
                    )
                  );
              },
                 
                ),
                ListTile(
                   title:new Text("Leaves"),
                  leading: Icon(Icons.assessment_outlined ),
                  onTap: (){
                Navigator.pop(context);
                  Navigator.push(context, new MaterialPageRoute(
                    builder: (context)=>new Leaves()
                    )
                  );
              },
                 
                )
                // Text("My Attendance"),
                // Text("Leaves"),
              ],
              leading: Icon(Icons.history,
            ),
            
            )],
        ),

      
    ),
 );
  }
}

这是我传递参数的 RequestforLeave 代码

import 'package:attendance_system_app/Admin_Navigation/AdminNavigation.dart';
import 'package:attendance_system_app/Employee_Navigation/EmployeeNavigation.dart';
import 'package:attendance_system_app/Leaves/Leaves.dart';
import 'package:attendance_system_app/My_Attendance/MyAttendance.dart';
import 'package:flutter/material.dart';

class RequestForLeave extends StatefulWidget {
  var name;
  var email;
  RequestForLeave(name, email);

  @override
  State<StatefulWidget> createState(){
     return _RequestForLeaveState(this.name,this.email);
     }
  
}

class _RequestForLeaveState extends State<RequestForLeave> {
  var name;
  var email;
_RequestForLeaveState(this.name,this.email);
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: AppBar(
       title: Image.asset("assets/image/company_logo.png",height: 140,width: 280,
       ),
      
       //automaticallyImplyLeading: false,
       backgroundColor: Colors.white,
       iconTheme: IconThemeData(color: Colors.blue,size: 20),
       //leading: new Icon(Icons.menu,color: Colors.blue,),
       actions: <Widget>[
       IconButton(
        icon: Icon(
        Icons.notifications,
        color: Colors.blue,
        size:26
      ),
      onPressed: () {
        // do something
      },
      
    )
    ],
    ),
    drawer:new  Drawer(
      child: new ListView(
          padding: const EdgeInsets.all(0.0),
          children: <Widget>[
            new UserAccountsDrawerHeader(
                accountName: new Text(name,style: TextStyle(fontSize: 14)),
                accountEmail: new Text(email,style: TextStyle(fontSize: 14),),
                currentAccountPicture: new CircleAvatar(
                  backgroundColor:
                  Theme.of(context).platform == TargetPlatform.android
                      ? Colors.white
                      : Colors.blue,
              child: Text(
                name[0][0],
                style: TextStyle(fontSize: 40.0),
              ),
            ),
          ),
            new ListTile(
              title: new Text('Request for leave'),
              leading: Icon(Icons.request_page),
              onTap: (){
                Navigator.pop(context);
                  Navigator.push(context, new MaterialPageRoute(
                    builder: (context)=>new RequestForLeave(name,email)
                    )
                  );
              },
            ),
            new ExpansionTile(
              title: new Text('History'),
              children: <Widget>[
                ListTile(
                   title:new Text("My Attendance"),
                  leading: Icon(Icons.assessment_outlined ),
                  onTap: (){
                Navigator.pop(context);
                  Navigator.push(context, new MaterialPageRoute(
                    builder: (context)=>new MyAttendance()
                    )
                  );
              },
                 
                ),
                ListTile(
                   title:new Text("Leaves"),
                  leading: Icon(Icons.assessment_outlined ),
                  onTap: (){
                Navigator.pop(context);
                  Navigator.push(context, new MaterialPageRoute(
                    builder: (context)=>new Leaves()
                    )
                  );
              },
                 
                )
                // Text("My Attendance"),
                // Text("Leaves"),
              ],
              leading: Icon(Icons.history,
            ),
            
            )],
        ),

      
    ),
      body:Center(
          child: Text(
        "Request for leave",
        style: TextStyle(fontSize: 28),
      )),
      
      
    );
  }
}

我在 EmployeeNavigation 抽屉上得到了正确的值，但是当我点击 Request for leave 时出现错误

这里是错误输出

[![在此处输入图片描述][1]][1]

这是我的主屏幕抽屉样子

[![在此处输入图片描述][2]][2]

请帮我解决这个问题，我在我的应用程序的每个屏幕上都显示相同的抽屉。

--------------------更新了-------------------- ----------

class EmployeeNavigation extends StatefulWidget {
  var name;
  var email;
  var designation;
  var date;
  var timeIn;
  var timeOut;
  EmployeeNavigation({this.name, this.email, this.designation, this.date, this.timeIn, this.timeOut, } );
  @override
  State<StatefulWidget> createState() {
    return EmployeeNavigationState(this.name,this.email,this.designation,this.date,this.timeIn,this.timeOut);
  }
}

class EmployeeNavigationState extends State<EmployeeNavigation> {

// here is create Drawer widget

 Widget DrawerCode(){
   return Drawer(
     child: new ListView(
          padding: const EdgeInsets.all(0.0),
          children: <Widget>[
            new UserAccountsDrawerHeader(
                accountName: new Text(name,style: TextStyle(fontSize: 14)),
                accountEmail: new Text(email,style: TextStyle(fontSize: 14),),
                currentAccountPicture: new CircleAvatar(
                  backgroundColor:
                  Theme.of(context).platform == TargetPlatform.android
                      ? Colors.white
                      : Colors.blue,
              child: Text(
                name[0][0],
                style: TextStyle(fontSize: 40.0),
              ),
            ),
          ),
            new ListTile(
              title: new Text('Request for leave'),
              leading: Icon(Icons.request_page),
              onTap: (){
                Navigator.pop(context);
                  Navigator.push(context, new MaterialPageRoute(
                    builder: (context)=>new RequestForLeave()
                    )
                  );
              },
            ),
            new ExpansionTile(
              title: new Text('History'),
              children: <Widget>[
                ListTile(
                   title:new Text("My Attendance"),
                  leading: Icon(Icons.assessment_outlined ),
                  onTap: (){
                Navigator.pop(context);
                  Navigator.push(context, new MaterialPageRoute(
                    builder: (context)=>new MyAttendance()
                    )
                  );
              },
                 
                ),
                ListTile(
                   title:new Text("Leaves"),
                  leading: Icon(Icons.assessment_outlined ),
                  onTap: (){
                Navigator.pop(context);
                  Navigator.push(context, new MaterialPageRoute(
                    builder: (context)=>new Leaves()
                    )
                  );
              },
                 
                )
                // Text("My Attendance"),
                // Text("Leaves"),
              ],
              leading: Icon(Icons.history,
            ),
            
            )],
        ),

      
    );

   
 }


var name;
  var email;
  var designation;
  var date;

 EmployeeNavigationState(this.name,this.email, this.designation,this.date,this.timeIn, this.timeOut );
   bool valuefirst = false;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
       title: Image.asset("assets/image/company_logo.png",height: 140,width: 280,
       ),

       backgroundColor: Colors.white,
       iconTheme: IconThemeData(color: Colors.blue,size: 20),
       //leading: new Icon(Icons.menu,color: Colors.blue,),
       actions: <Widget>[
       IconButton(
        icon: Icon(
        Icons.notifications,
        color: Colors.blue,
        size:26
      ),
     
      
    )
    ],
    ),
    drawer:DrawerCode(),
 );
  }
}




  [1]: https://i.stack.imgur.com/aAqI2.png
  [2]: https://i.stack.imgur.com/Ivpbu.png

Answer 1

显示的错误与抽屉无关，它与您将 NULL 传递到需要有效字符串的 Text 小部件有关。

String variable = null;
Text(variable) <-- error

String variable = '';
Text(variable) <-- fine!

对我来说，您采用的方法似乎不正确。如果你有 100 个屏幕并且你想在每个屏幕中显示抽屉，你将有 100 个抽屉。如果您喜欢这种方法，您应该创建一个 Drawer Widget 文件以避免重复。

我可以建议您采用不同的方法吗？

假设您有以下文件夹结构：

 Home Screen
    - Dashboard Screen
    - Customers Screen
    - Items Screen

只有Home Screen有抽屉。 Home Screen 将在其内部加载所有子屏幕（仪表板、客户和项目）。

class _HomeState extends State<Home> 
{
    String appTitle = 'Dashboard';
    Widget appBody = DashboardScreen(); // By default

    @override
    Widget build(BuildContext context) {
        return Scaffold(
          appBar: AppBar(
            title: Text(
              this.appTitle,
            ),
          ),
          body: this.appBody,
          drawer: YourDrawer()
        );
    }
}

现在你所需要的只是一个随时跳转到另一个子屏幕的功能：

void jumpToScreen(String appTitle, Widget appBody)
{
    setState(()
    {
        this.appTitle = appTitle;
        this.appBody = appBody;
    });
}

您还可以应用一些逻辑来根据屏幕显示不同的应用程序操作按钮。

如何在 flutter 的应用程序的每个屏幕上显示名称和电子邮件

How to display name and email on every screen of app in flutter

mongodb

drawer

flutter