Updating label if value in singleton changes - ios

Question

I am getting some user information from Firebase and storing it into singleton. After that every time the value changes I want that the label changes also but it doesn't until I terminate the app and come back in.
How should I update label if value changes in singleton?
I have tab views. In first tab I assign values and in second tab I try to put the values to label.
This is my singleton:
class CurrentUser: NSObject
{
var generalDetails: User = User()/// Consecutive declarations on a line must be separated by ';'
static let sharedInstance = CurrentUser()
fileprivate override init(){
super.init()
}
}
And like this I assign values:
self.databaseRef.child("users").child(user.uid).observeSingleEvent(of: .value) { (snapshot:FIRDataSnapshot) in
guard let firebaseValue = snapshot.value as? [String:AnyObject], let userName = firebaseValue["username"] as? String, let email = firebaseValue["email"] as? String, let reputation = firebaseValue["reputation"] as? Int, let profilePicURL = firebaseValue["profileImageUrl"] as? String
else
{
print("Error with FrB snapshot")//Here
return
}
//Set values
self.currentUser.generalDetails = User(userName: userName, email: email, reputation: reputation, profileImageURL: profilePicURL, uid: user.uid)
}
And if I want to put the value to the label I simply do this(This reputation is the only thing that can change often):
self.reputationLabel.text = String(self.currentUser.generalDetails.reputation)

Answer 1

You can do either of these:-
Communicate between the singleton and your class with delegate-protocol method , fire the delegate method in the class whenever your repo changes and update your label.
Open a different thread in your network link for the user's reputation in the viewController itself:-
override func viewDidLoad() {
super.viewDidLoad()
FIRDatabase.database().reference().child("users").child(FIRAuth.auth()!.currentUser!.uid).child("reputation").observe(.childChanged, with: {(Snapshot) in
print(Snapshot.value!)
//Update yor label
})
which will get called every time the value of reputation changes.

Answer 2

I like Dravidian's answer and I would like to offer an alternative: KVO
We use Key-Value Observing to monitor if our app is disconnected from the Firebase server. Here's the overview.
We have a singleton which stores a boolean variable isConnected, and that variable is set by observing a special node in Firebase
var isConnected = rootRef.child(".info/connected")
When connected/disconnected, the isConnected var changes state.
We have a little icon on our views that indicates to the user the connected state; when connected it's green, when disconnected it's red with a line through it.
That icon is a class and within each class we have code that observes the isConnected variable; when it's state changes all of the icons change automatically.
It takes very little code, is reusable, is clean and easily maintained.
Here's a code snippet from the Apple documentation
//define a class that you want to observe
class MyObjectToObserve: NSObject {
dynamic var myDate = NSDate()
func updateDate() {
myDate = NSDate()
}
}
//Create a global context variable.
private var myContext = 0
//create a class that observes the myDate var
// and will be notified when that var changes
class MyObserver: NSObject {
var objectToObserve = MyObjectToObserve()
objectToObserve.addObserver(self,
forKeyPath: "myDate",
options: .new,
context: &myContext)
There will be more to it but that's it at a 10k foot level.
The Apple documentation is here
Using Swift with Cocoa and Obj-c 3.01: Design Patterns
and scroll down the the Key-Value Observing Section. It's a good read and very powerful. It follows the same design pattern as Firebase (or vice-versa) - observe a node (variable) and tell me when it changes.