Flutter and Firebase: How can i receive data from function? - dart

Question

i use the following function to fetch userData from Firestore:
Future<String>getRegisterUserData({String userID}) async {
Firestore.instance.collection("Users").document(userID).get().then(
(datasnapshot) {
if (datasnapshot.exists) {
return datasnapshot.data['Email'];
} else {
return "Loading...";
}
},
);
}
I execute this function on my UserProfilePage like this:
_email = widget.firestore.getRegisterUserData(widget.userID).toString();
But i always get the print statement: Instance of 'Future' and not the saved email-address...
i also try this:
Future<String> getRegisterUserData({String userID}) async {
String email;
Firestore.instance.collection("Users").document(userID).get().then(
(datasnapshot) {
if (datasnapshot.exists) {
email = datasnapshot.data['Email'];
} else {
email = "Loading...";
}
},
);
return email;
}
The Print Statement is always the same...
So where is my mistake? I want to display the Value of 'Email' on the UserProfilePage in a variable, or is my firestore function incorrect?
Thank you for our help

Answer 1

Add await keyword. But at a different place.
tempEmail = await widget.firestore.getRegisterUserData(widget.userID);
setState(() {
_email = tempEmail;
});
// we don't need toString as getRegisterUserData itself is returning Future<String>
Note for using await: As we are using await the method/function which contains this should have a async in its signature.
Or you can use then block
widget.firestore.getRegisterUserData(widget.userID).then((email) {
setState(() {
_email = email;
});
});
Explanation: widget.firestore.getRegisterUserData(widget.userID) is of type Future<String>. that's why it is printed as Instance of 'Future'. We have to convert the Future to String by await or by then block
Using SharedPreferences:
Future<String> getEmail() async {
final prefs = await SharedPreferences.getInstance();
String email = prefs.getString('email');
if (email != null) {
return email;
} else {
email = await widget.firestore.getRegisterUserData(widget.userID);
prefs.setString('email', email); //update shared preferences
return email;
}
}
// usage (may be in initState)
widget.getEmail().then((email) {
setState(() {
_email = email;
})
})

Answer 2

Updated
Based on your information, you need a FutureBuilder in order to wait the response to build your widget:
return FutureBuilder(
future: getRegisterUserData(userID: "1234"),
builder: (context, asyncsnapshot){
return asyncsnapshot.hasData && asyncsnapshot.data != null ? TextFormField(
initialValue: asyncsnapshot.data,
) : CircularProgressIndicator();
}
);