等待firebase加载直到显示View

Question

I'm currently building an app and i faced some issues. I use Firebase to store the user data and then i display it in some of the views, i managed to create the function to retrieve data with completion, so the async issue is solved, but now when i need to display some of the data it displays nil, because the view is loaded sooner than the firebase loads.

My function to load data from firebase:

func getUserFromUID(completion: @escaping (UserData)->()){
    
    
    ref.child("users").child(uid).observe(.value) { (snapshot) in
        DispatchQueue.main.async {
            guard let dictionary = snapshot.value as? [String:AnyObject]  else { return}
            
            var user = UserData()
            
            if let email = dictionary["email"]{ user.email = email  as? String }
            if let name = dictionary["name"]{ user.name = name  as? String }
            user.firstname = (dictionary["firstname"] as! String)
            user.lastname = (dictionary["lastname"] as! String)
            user.type = (dictionary["type"] as! String)
            user.uid = (dictionary["uid"] as! String)
            user.profileImageUrl = (dictionary["profileImageUrl"] as! String)
            user.id = snapshot.key
            user.fcmToken2 = (dictionary["fcmToken"] as! String)
            
            
            completion(user)
        }
    }
    
}

ChatsHomeView:

struct ChatsHomeView: View {
    
    @ObservedObject var session : SessionStore
    @State var user = UserData()
    
    func getUserInfo(){
        session.getUserFromUID { (fetcheduser) in
            self.user = fetcheduser
            print("THE USER:\(user)")
        }
    }
    
    var body: some View {
        
        VStack{
            
            Text(user.name ?? "nil")
            Button(action: {
                session.signOut()
            }){ Text("Logout").padding() }
        }.onAppear{
            getUserInfo()
        }
    }
}

The problem is, that once the user logins, it displays nil where the ChatsHomeView Text(user.name?? "nil") field is. I need to restart the app for the field to update and show the Name. Is there a way to show the app launch screen until firebase fully loads, or maybe there is any other way?

Answer 1

The iOS app will certainly be ready to show views before any.network operation completes.

The requirement to keep a launch screen visible can be met by having the first VC's UI match the launch view. I've done this in an Objective-C app. In it, that first VC loads the launch view's nib in viewDidLoad and sets it as the view.

The completion code for the user snapshot should then check to see if the launch UI is still visible. If it is, it can then change the UI then to one that expects the user data.

edit Illustration from an Objective-C project:

In the first VC designated in the main storyboard, grab the UI from your app's launch storyboard and temporarily cover your view with it. The user perception will be that the launch is still happening. Kick off the async work. When it completes, change the UI back...

- (void)viewDidLoad {
    [super viewDidLoad];
    
    NSString *storyboardName = [[NSBundle mainBundle] objectForInfoDictionaryKey:@"UILaunchStoryboardName"];
    UIStoryboard *storyboard = [UIStoryboard storyboardWithName:storyboardName bundle:nil];
    UINavigationController *vc = [storyboard instantiateViewControllerWithIdentifier:@"LaunchVC"];
    UIView *launchView = vc.view;
    
    [self.view addSubview:launchView];
    [self startObserving:^(FIRDocumentSnapshot *snapshot, NSError *error) {
        if (!error) {
          // the async work has completed
          // setup this VC's underlying view with data from the snapshot, then uncover it
          [launchView removeFromSuperview]; 
        }
    }];
}

Answer 2

why not to on firebase offline capability it help you out to auto sync current data and also it will not load to again and again all data

you need to enable isPersistenceEnabled property for your firebase database

Database.database().isPersistenceEnabled = true

then you need to use keepSynced(true) so the data will stay synchronized.

Persistence Behavior:

By enabling persistence, any data that the Firebase Realtime Database client would sync while online persists to disk and is available offline, even when the user or operating system restarts the app. This means your app works as it would online by using the local data stored in the cache. Listener callbacks will continue to fire for local updates.

keepSynced(true):

The Firebase Realtime Database synchronizes and stores a local copy of the data for active listeners. In addition, you can keep specific locations in sync.

for more info check this documentation