App "freezes" when opening VC and getting data from Firebase - ios

Question

I have run into a problem behaving like this. When opening a new VC which is getting a few pictures from Firebase Storage (in this case 9 pictures, each picture being a few KB) and getting a small number of documents from Firestore, the app sort of freezes for about 2-4 seconds before opening and showing the view. I have a tab bar controller and I'm unable to tap on any other tab bar element until the view has shown up.
I have all my Firebase references and calling the function inside viewWillAppear I have also tried putting everything inside ViewDidLoad and viewDidAppear, but I'm experiencing the same freeze.
Is there a solution for this, am I doing something wrong or do I just have to live with this?
I have the latest Firebase version, I'm using swift 4 and have a 1000mb internet connection.
var db: Firestore!
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(true)
tableView.delegate = self
tableView.dataSource = self
db = Firestore.firestore()
getTasks()
tableView.reloadData()
}
func getTasks() {
db.collection("School").document(school).collection("Projects").document((project?.projectId)!).collection("Tasks").whereField("Completed", isEqualTo: false).addSnapshotListener { (snapshot, error) in
if let error = error {
print(error)
} else {
self.tasks = snapshot!.documents.compactMap({TaskModel(dictonary: $0.data())})
self.tableView.reloadData()
}
}
}

Answer 1

It seems like you are fetching data from main thread(which blocks the UI). use GCD for fetching data async and then reload your table view.
DispatchQueue.global(qos: .background).async {
self.getTasks()
DispatchQueue.main.async {
self.tableView.reloadData()
}
}

Answer 2

See your code fetches all the images before presenting that view that's why it freezes. If you have used firebase you must understand that it downloads all the subnodes present in your main node.
Solution:- One way to solve the freezing thing is to call the 'getTasks()' function in ' viewdidAppear() ' function. So you would be able to access your view while it would simultaneously loads the data. Also You can use activity indicator to indicate that the data is downloading.