Flutter - How to complete/await function execution before build method? - flutter

Question

I am simply trying to set an ID in this function:
_getLastWorkoutId() async {
try {
var snapshot = await usersRef
.doc(currentUser!.uid)
.collection('workouts')
.orderBy('workoutDate', descending: true)
.limit(1)
.snapshots()
.first;
//The execution moves to build method from here------and then returns
for (var element in snapshot.docs) {
workoutId = element.id;
setState(() {
_isWorkoutIdSet = true;
});
}
//return snapshot;
} catch (e) {
print(e.toString());
}
//return null;
}
I call it in the initState:
#override
void initState() {
WidgetsBinding.instance!.addObserver(this);
super.initState();
//var snapshot = _getLastWorkoutId();
_getLastWorkoutId();
}
The problem is, the for loop executes after the build function is called. I don't want that to happen.

Answer 1

You can use FutureBuilder like this:
Future<bool> _value;
#override
void initState() {
WidgetsBinding.instance!.addObserver(this);
super.initState();
_value = _getLastWorkoutId();
}
And in your build method you have:
FutureBuilder<bool>(
future: _value,
builder: (
BuildContext context,
AsyncSnapshot<bool> snapshot,
) {
if (snapshot.hasData) {
if (snapshot.data){
//update view
}else{
//update view
}
}
}
The method can be like this:
_getLastWorkoutId() async {
try {
var snapshot = await usersRef
.doc(currentUser!.uid)
.collection('workouts')
.orderBy('workoutDate', descending: true)
.limit(1)
.snapshots()
.first;
for (var element in snapshot.docs) {
workoutId = element.id;
return true;
}
} catch (e) {
print(e.toString());
}
}
Here you can find more about FutureBuilder.

Answer 2

I believe this should solve the issue:
First, on build method:
return FutureBuilder(
future: _getLastWorkoutId(),
builder: (context, snapshot) {
if (snapshot.connectionState != ConnectionState.done) return CircularProgressIndicator();
return Container(); // here goes whatever it is you had before.
}
);
then on _getLastWorkoutId():
Future<void> _getLastWorkoutId() async {
...
}
That way the function returns a future of void instead of void, allowing FutureBuilder to do its thing.

Answer 3

You should declare a variable to save state. For example
var isLoading = true;
At the end of try block in func _getLastWorkoutId reset isLoading to false.
Then call setState or update state by better way used state management likes provider, bloc, get.
In build widget add check isLoading like this
return isLoading ? YourLoadingIndicatorWidget() : DisplayDataWidget();