Error While retrieving the number of Firebase collections in Flutter? - firebase

Question

I'm developing an admin app in that i want to display the number of users(Collection) from the cloud firestore. When i tried doing this im able print the value in my terimal but its displaying 0 in my app.
Can someone please help in this, this my code
class _AdminState extends State<Admin> {
getUsersCount() {
var length = 0;
Firestore.instance.collection('users').getDocuments().then((myDocuments){
print("${myDocuments.documents.length}");
length = myDocuments.documents.length;
});
return length.toString();
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Row(
children: <Widget>[
Expanded(
child: FlatButton.icon(
onPressed: () {
setState(() => _selectedPage = Page.dashboard);
},
icon: Icon(
Icons.dashboard,
color: _selectedPage == Page.dashboard
? active
: notActive,
),
label: Text('Dashboard'))),
Expanded(
child: FlatButton.icon(
onPressed: () {
setState(() => _selectedPage = Page.manage);
},
icon: Icon(
Icons.sort,
color:
_selectedPage == Page.manage ? active : notActive,
),
label: Text('Manage'))),
],
),
elevation: 0.0,
backgroundColor: Colors.white,
),
body: _loadScreen());
}
Widget _loadScreen() {
switch (_selectedPage) {
case Page.dashboard:
return Column(
children: <Widget>[
ListTile(
subtitle: Text(
'Admin View',
textAlign: TextAlign.center,
style: TextStyle(fontSize: 29.0, color: Colors.indigo,fontWeight: FontWeight.bold),
),
),
Expanded(
child: GridView(
gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
crossAxisCount: 2,
),
children: <Widget>[
Padding(
padding: const EdgeInsets.all(18.0),
child: Card(
child: ListTile(
title: FlatButton.icon(
onPressed: null,
icon: Icon(Icons.directions_boat,color: Colors.black,),
label: Text("Boats",style: TextStyle(fontSize: 9,color: Colors.indigo),)),
subtitle: Text(
'3',
textAlign: TextAlign.center,
style: TextStyle(color: active, fontSize: 50.0),
)),
),
),
Padding(
padding: const EdgeInsets.all(18.0),
child: Card(
child: ListTile(
title: FlatButton.icon(
onPressed: null,
icon: Icon(Icons.people,color: Colors.black,),
label: Text("Users",style: TextStyle(fontSize: 9,color: Colors.indigo),)),
subtitle: Text(
getUsersCount(),
textAlign: TextAlign.center,
style: TextStyle(color: active, fontSize: 50.0),
)),
),
),
Padding(
padding: const EdgeInsets.all(22.0),
child: Card(
child: ListTile(
title: FlatButton.icon(
onPressed: null,
icon: Icon(Icons.bookmark,color: Colors.black,),
label: Text("Bookings",style: TextStyle(fontSize: 8,color: Colors.indigo),)),
subtitle: Text(
'120',
textAlign: TextAlign.center,
style: TextStyle(color: active, fontSize: 50.0),
)),
),
),
],
),
),
],
);
break;
My terminal is printing the exact value which is available in the database.the terminal looks like this
My screenshot of the app looks like this
Padding(
padding: const EdgeInsets.all(18.0),
child: Card(
child: ListTile(
title: FlatButton.icon(
onPressed: null,
icon: Icon(Icons.people,color: Colors.black,),
label: Text("Users",style: TextStyle(fontSize: 9,color: Colors.indigo),)),
subtitle: Text(
getUsersCount(),
textAlign: TextAlign.center,
style: TextStyle(color: active, fontSize: 50.0),
)),
),
),

Answer 1

getDocuments() is asychronous, then you need to return a value of type Future to be able to get the returned value later:
Future<String> getUsersCount() {
var length = 0;
Firestore.instance.collection('users').getDocuments().then((myDocuments){
print("${myDocuments.documents.length}");
length = myDocuments.documents.length;
});
return Future.value(length.toString());
}
Then when you call it, you can do:
getUsersCount().then((value){
print(value);
});