Flutter how to use multiple forloops - flutter

Question

I am using this code but sometimes it runs the code in wrong order. Is it possible to wait for each for loop to finish before next one starts?
void changeWeek() {
for (int i = 0; i < newactivities.length; i++) {
int year = DateTime.now().year;
DateTime startDate = DateTime(year, 1, 1);
while (startDate.weekday != DateTime.monday) {
startDate = startDate.add(const Duration(days: 1));
}
for (String weekday in newactivities[i].daylistdone) {
int offset = (int.parse(weekday)) + (int.parse(currentweek) - 1) * 7;
DateTime donedate = startDate.add(Duration(days: offset));
oldDatesDone.add(Timestamp.fromDate(donedate));
}
for (String weekday in newactivities[i].daylist) {
int offset =
(int.parse(weekday) - 1) + (int.parse(currentweek) - 1) * 7;
DateTime notdonedate = startDate.add(Duration(days: offset));
oldDatesNotDone.add(Timestamp.fromDate(notdonedate));
}
for (var i in oldDatesDone) {
oldDatesNotDone.remove(i);
}
finaloldDatesDone = newactivities[i].weekdaysdone + oldDatesDone;
finaloldDatesNotDone = newactivities[i].weekdaysnotdone + oldDatesNotDone;
act.add({
'title': newactivities[i].title,
'days': newactivities[i].daylist,
'notificationidnumber': newactivities[i].notificationidnumber,
'daysdone': myData22,
'weekdaysdone': finaloldDatesDone,
'weekdaysnotdone': finaloldDatesNotDone,
'timelist': newactivities[i].timelist,
'time': newactivities[i].time
});
FirebaseFirestore.instance
.collection(widget.user.user.uid)
.doc(documentName)
.update({"activities": act});
}
}
Or can I do it in another way to solve the code?

Answer 1

Your Firebase update returns a Future, so it is an asynchronous operation. To preserve order of calls, you need to await the result of this call:
void changeWeek() async {
// ...
await FirebaseFirestore.instance
.collection(widget.user.user.uid)
.doc(documentName)
.update({"activities": act});
}
Note that you need do declare the changeWeek() function as async for this to work.