我正在处理在线公告板项目，我使用以下代码上传通知上传正在工作，但它给出了以下错误。
class UploadNotice extends StatefulWidget {
@override
_UploadNoticeState createState() => _UploadNoticeState();
}
class _UploadNoticeState extends State<UploadNotice> {
final _formKey=GlobalKey<FormState>();
final List<String> noticrcategory=
['Exams','Mahapola/Bursary','TimeTables','Results','Other','General'];
File _noticepic;
String title;
String url;
String category;
String dateTime;
var uuid=Uuid();
bool loading = false;
DateTime now=new DateTime.now();
@override
Widget build(BuildContext context) {
Future getImage() async{
var image=await ImagePicker.pickImage(source: ImageSource.gallery);
setState(() {
_noticepic=image;
print('image path: $_noticepic');
});
}
Future uploadPic(BuildContext context)async{
String fileName=basename(_noticepic.path);
final StorageReference firebaseStorageRef=FirebaseStorage()
.ref().child('notices/$fileName');
final StorageUploadTask uploadTask=firebaseStorageRef.putFile(_noticepic);
StorageTaskSnapshot taskSnapshot= await uploadTask.onComplete;
String downloadurl = await taskSnapshot.ref.getDownloadURL();
url=downloadurl.toString();
}
final user = Provider.of<User>(context);
return StreamBuilder(
stream:UserService(uid: user.uid).userData,
builder: (context,snapshot){
User userData=snapshot.data;
String getDepartmentName(){
return userData.department.toString();
}
String department=getDepartmentName();
return loading ? Loading(): Scaffold(
appBar: AppBar(
elevation: 0.0,
title: Text('Notices App',
style: TextStyle(
fontFamily: 'Montserrat',
fontWeight: FontWeight.bold,
color: Colors.white,
),
),
backgroundColor: Colors.blue[800],
),
body:SingleChildScrollView(
child: Padding(
padding: const EdgeInsets.all(8.0),
child: Form(
key: _formKey,
child: Column(
children: <Widget>[
Padding(
padding: const EdgeInsets.all(10.0),
child: Container(child: Text('Add your notice here')
),
),
Container(
child:(_noticepic!=null)?Image.file(_noticepic,fit: BoxFit.fill):
Image.asset('',),
height: 450.0,
width:300.0,
color: Colors.grey[400],
),
Padding(
padding: const EdgeInsets.only(left: 280),
child: Container(
child: IconButton(
icon: Icon(Icons.add_photo_alternate),
color: Colors.grey[700],
iconSize: 40,
onPressed:(){
getImage().then((context){
uploadPic(context);
});
}
),
),
),
TextFormField(
decoration: new InputDecoration(labelText: 'Title'),
validator: (value) {
return value.isEmpty ? 'Title is Required' : null;
},
onChanged: (value) {
setState(() => title = value);
}),
DropdownButtonFormField(
value: category ?? 'General',
items: noticrcategory.map((noticrcategory){
return DropdownMenuItem(
value: noticrcategory,
child: Text('$noticrcategory Category'),
);
}).toList(),
onChanged: (value)=>setState(()=>category=value),
),
Text('${now.day}/${now.month}/${now.year}'),
SizedBox(height: 30.0,),
Container(
height: 30.0,
width: 100.0,
child: RaisedButton(
onPressed: () async {
setState(() => loading=true);
await NoticeService().updteNoticeData(
title,
url,
category,
'unapproved',
now,
'$department',
uuid.v4());
Navigator.of(context).pushReplacementNamed('/Upload Notices');
},
child: Text('Upload',style: TextStyle(color: Colors.white),),
color: Colors.blue[700],
),
)
],
),
),
),
),
);
}
);
}
这是这里的代码，我可以将通知作为图像上传，我可以将当前时间上传到 Firestore。firestore 记录由此代码创建。但它给出了以下错误。
════════ Exception caught by widgets library ═══════════════════════════════════
The getter 'department' was called on null.
Receiver: null
Tried calling: department
The relevant error-causing widget was
StreamBuilder<User>
lib\…\pages\uploadNotice.dart:56
════════════════════════════════════════════════════════════════════════════════
════════ Exception caught by image resource service ════════════════════════════
Unable to load asset:
════════════════════════════════════════════════════════════════════════════════