while retrieving data from firebase in a flutter app - flutter

Question

This is the code
import 'package:flutter/material.dart';
import 'Authentication.dart';
import 'photoUpload.dart';
import 'Posts.dart';
import 'package:firebase_database/firebase_database.dart';
// import 'package:flutter_blogapp/Authentication.dart';
// import 'package:flutter_blogapp/photoUpload.dart';
class HomePage extends StatefulWidget
{
HomePage
(
{
this.auth,
this.onSignedOut,
}
);
final AuthImplementation auth;
final VoidCallback onSignedOut;
#override
State<StatefulWidget> createState()
{
return _HomePageState();
}
}
class _HomePageState extends State<HomePage>
{
List<Posts> postsList = [];
#override
void initState()
{
super.initState();
DatabaseReference postsRef = FirebaseDatabase.instance.reference().child("Posts");
postsRef.once().then((DataSnapshot snap)
{
var KEYS = snap.value.keys;
var DATA = snap.value;
postsList.clear();
for(var individualKey in KEYS)
{
Posts posts = new Posts
(
DATA[individualKey]['image'],
DATA[individualKey]['desctiption'],
DATA[individualKey]['data'],
DATA[individualKey]['time'],
);
postsList.add(posts);
}
setState(()
{
print('Length : $postsList.length');
});
});
}
void _logoutUser() async
{
try
{
await widget.auth.signOut();
widget.onSignedOut();
}
catch (e)
{
print(e.toString());
}
}
#override
Widget build(BuildContext context)
{
return new Scaffold
(
appBar: new AppBar
(
title: new Text('Home'),
),
body : new Container
(
child: postsList.length == 0 ? new Text(" No Post available ") : new ListView.builder
(
itemCount: postsList.length,
itemBuilder: (_, index)
//itemBuilder: (BuildContext _, int index ) //<-----
{
return PostsUI(postsList[index].image, postsList[index].description, postsList[index].date, postsList[index].time);
}
),
),
bottomNavigationBar: new BottomAppBar
(
color: Colors.pink,
child: new Container
(
margin: const EdgeInsets.only(left: 70.0, right: 70.0),
child: new Row
(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
mainAxisSize: MainAxisSize.max,
children: <Widget>
[
new IconButton
(
icon: new Icon(Icons.local_car_wash),
iconSize: 50,
color: Colors.white,
onPressed: _logoutUser,
),
new IconButton
(
icon: new Icon(Icons.add_a_photo),
iconSize: 50,
color: Colors.white,
onPressed: ()
{
Navigator.push
(
context,
MaterialPageRoute(builder: (context)
{
return new UploadPhotoPage();
})
);
},
),
],
),
),
),
);
}
// Designing Posts UI <remove from Text field><??'defaut value'>
Widget PostsUI(String image, String description, String date, String time)
{
return new Card
(
elevation: 10.0,
margin: EdgeInsets.all(15.0),
child: new Container
(
padding: new EdgeInsets.all(14.0),
child: new Column
(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>
[
new Row
(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>
[
new Text
(
date,
style: Theme.of(context).textTheme.subtitle,
textAlign: TextAlign.center,
),
new Text
(
time,
style: Theme.of(context).textTheme.subtitle,
textAlign: TextAlign.center,
), //<----
],
),
SizedBox(height: 10.0,),
new Image.network(image, fit:BoxFit.cover),
SizedBox(height: 10.0,),
new Text
(
description, //= null ? "true" : "False", //??'defaut value'
style: Theme.of(context).textTheme.subhead,
textAlign: TextAlign.center,
),
],
)
)
);
}
}
The error that i was getting
The following assertion was thrown building: A non-null String must be
provided to a Text widget. 'package:flutter/src/widgets/text.dart':
Failed assertion: line 285 pos 10: 'data != null'
Either the assertion indicates an error in the framework itself, or we
should provide substantially more information in this error message to
help you determine and fix the underlying cause. In either case,
please report this assertion by filing a bug on GitHub:
https://github.com/flutter/flutter/issues/new?template=BUG.md
When the exception was thrown, this was the stack
2 new Text package:flutter/…/widgets/text.dart:285
3 _HomePageState.PostsUI package:flutter_blogapp/HomePage.dart:184
4 _HomePageState.build. package:flutter_blogapp/HomePage.dart:100
5 SliverChildBuilderDelegate.build package:flutter/…/widgets/sliver.dart:446
6 SliverMultiBoxAdaptorElement._build. package:flutter/…/widgets/sliver.dart:1260
What can i do to retrieve the data in my app? I have tried what i can do. can some one help me in finding where am I wrong? I have started learning recently.

Answer 1

First thing, pull the code out of the initState and put in a different function. This will keep your initState clean.
What I can see is you're trying to update data in firestore.
What you could do is define a new function as follows:
final databaseReference = Firestore.instance;
setPostsData() async {
DocumentSnapshot snapshot = await databaseReference
.collection("NAME_OF_COLLECTION")
.document("NAME_OF_DOCUMENT")
.get();
// use this DocumentSnapshot snapshot to get the current data that is there in the document inside of your collection.
var currentData = snapshot.data;
print(currentData); // to check whats actually there and if its working...
//lets assume newPostsList is the data that you want to put in this referenced document.
//to update the data in firestore:
await databaseReference
.collection("NAME_OF_COLLECTION")
.document("NAME_OF_DOCUMENT")
.updateData({newPostsList});
}
Then you can put setPostsData in the initState.
For this to work, you might want to redesign your database structure, for example: it should be like users --> posts --> List_of_all_posts. If did this way, NAME_OF_COLLECTION will be users and NAME_OF_DOCUMENT will be posts.