Async Functions: Future<Query Snapshot> to Bool in Flutter? - firebase

Question

I have this piece of code right here: if the user exists in the database and it's followed by the CurrentUser it builds an "Unfollow" custom button, otherwise it builds a follow button
CustomButton follow = CustomButton("Follow", Colors.red, Colors.red, Colors.white, user);
CustomButton unfollow = CustomButton("Unfollow", Colors.black, Colors.black, Colors.white, user);
AvatarHeader(user.username, " ", user.photoURL, checkIfFollowing(user.id)== true ? unfollow : follow)
the checkIfFollowing() function is always evaluated false probably because I have a problem in this asyncronus function which does not return a boolean value
checkIfFollowing(String fetchedUser) async{
DocumentSnapshot doc = await FOLLOWERS
.document(fetchedUser)
.collection('userFollowers')
.document(CURRENTUSER.id)
.get()
return doc.exists;
}
How can i fix this?
EDIT
search(String query) {
Future<QuerySnapshot> users = USERS
.where("username", isGreaterThanOrEqualTo: query)
.getDocuments();
print(query);
print("");
onStringChange(users);
}
FutureBuilder buildResults(){
return FutureBuilder (
future: results,
builder: (context, snapshot) {
if (!snapshot.hasData) {
print("i dont have data");
return circularProgress();
}
List<AvatarHeader> searchResults = [];
snapshot.data.documents.forEach((doc) async {
User user = User.fromDocument(doc);
if (user.photoURL != null) {
print(user.username);
bool check = await checkIfFollowing(user.id);
CustomButton follow = CustomButton("Follow", Colors.red, Colors.red, Colors.white, user);
CustomButton unfollow = CustomButton("Unfollow", Colors.black, Colors.black, Colors.white, user);
searchResults.add(AvatarHeader(user.username, " ", user.photoURL, check == true ? unfollow : follow));
}
});
return ListView(
shrinkWrap: true,
physics: ClampingScrollPhysics(),
children: searchResults,
);
},
);
}

Answer 1

You need to return a Future in async functions, in your particular case you need a Future<bool>
Future<bool> checkIfFollowing(String fetchedUser) async{
DocumentSnapshot doc = await FOLLOWERS
.document(fetchedUser)
.collection('userFollowers')
.document(CURRENTUSER.id)
.get()
return doc.exists;
}
I recommend you to take a look to Asynchronous programming: futures, async, await
A future (lower case “f”) is an instance of the Future (capitalized “F”) class. A future represents the result of an asynchronous operation, and can have two states: uncompleted or completed.
EDIT
Without more details is very hard to be sure how to solve your specific issue. If I understand correctly, you need to have something in line with this
FutureBuilder buildResults() {
return FutureBuilder(
future: results,
builder: (context, snapshot) {
if (!snapshot.hasData) {
print("i dont have data");
return circularProgress();
}
// get documents where user.photoURL != null
var docsWhereUserPhotoIsNotNull = getDocumentsWithUserPhotoNotNull(snapshot.data.documents);
// build a list of FutureBuilders
return ListView.builder(
shrinkWrap: true,
physics: ClampingScrollPhysics(),
itemCount: docsWhereUserPhotoIsNotNull.length,
itemBuilder: (context, index) {
var doc = docsWhereUserPhotoIsNotNull[index];
var user = User.fromDocument(doc);
return FutureBuilder(
future: checkIfFollowing(user.id),
builder: (context, snapshot) {
if (!snapshot.hasData) {
return circularProgress();
}
bool check = snapshot.data;
CustomButton follow = CustomButton("Follow", Colors.red, Colors.red, Colors.white, user);
CustomButton unfollow = CustomButton(
"Unfollow", Colors.black, Colors.black, Colors.white, user);
return AvatarHeader(user.username, " ", user.photoURL, check == true ? unfollow : follow);
});
});
}
);
}
Where
List<DocumentSnapshot> getDocumentsWithUserPhotoNotNull(List<DocumentSnapshot> documents) {
var documentsWithUserPhotoNotNull = List<DocumentSnapshot>();
documents.forEach((doc) async {
User user = User.fromDocument(doc);
if (user.photoURL != null) {
documentsWithUserPhotoNotNull.add(doc);
}
});
return documentsWithUserPhotoNotNull;
}