How to pull data point from Firebase using Obj-C? - objective-c

Question

I'm saving a users zip code to the Firebase database and want to query that database on app launch to see if the user has input their zip code already or if they're a brand new user.
I've posted my code before. I pulled the sample code from the Firebase docs, but it seems that my app is never even running the following code to get the value
[[[_ref child:#"user"] child:userID] observeSingleEventOfType:FIRDataEventTypeValue withBlock:^(FIRDataSnapshot * _Nonnull snapshot) {...
What am I missing out on?
#import "FollowingVC.h"
#import <FirebaseDatabase/FirebaseDatabase.h>
#import Firebase;
#interface FollowingVC ()
#property NSString *uid;
#property FIRDatabaseReference *ref;
#property NSString *zipcode;
#end
#implementation FollowingVC
- (void)viewDidLoad {
[super viewDidLoad];
[self createAuthorizedUser];
[self checkForZipCode];
}
-(void)createAuthorizedUser
{
[[FIRAuth auth]
signInAnonymouslyWithCompletion:^(FIRUser *_Nullable user, NSError *_Nullable error) {
if (!error) {
self.uid = user.uid;
self.ref=[[FIRDatabase database]reference];
}
}];
}
-(void)checkForZipCode
{
NSString *userID = [FIRAuth auth].currentUser.uid;
[[[_ref child:#"user"] child:userID] observeSingleEventOfType:FIRDataEventTypeValue withBlock:^(FIRDataSnapshot * _Nonnull snapshot) {
// Get user value
self.zipcode = snapshot.value[#"zip code"];
NSLog(#"It worked: %#", self.zipcode);
// ...
} withCancelBlock:^(NSError * _Nonnull error) {
NSLog(#"%#", error.localizedDescription);
}];
}
#end

Answer 1

Firebase is asynronous and you need to allow time for events to complete before moving on in the app.
In this case, you should call [self checkForZipCode] inside the sign-in block after self.uid is populated.
Otherwise you run the risk of the checkForZipCode function running before the self.uid is populated.
Let Firebase control the flow of the app - and don't try to use Firebase synchronously as it will get you into trouble due to internet lag etc.