Cannot retrieve recently added values with Firebase

Question

I have two view controllers in my app: the first one displays items pulled from a Firebase database, and the second one lets users add and remove items from the database.

The problem is when a user adds an item in the second view controller and goes back to the first controller really fast. This will sometimes cause the Firebase database not save the item. As a consequence the first view controller won't to display the newly added items.

As far as the implantation goes, I fetch items in viewWillAppear and then remove the Firebase listener observer in viewDidDisappear. How can I fix this?

// first view controller code

var items = [Item]()

var ref: FIRDatabaseReference!

func fetchItems() {
    ref.child("items").observeSingleEvent(of: .value, with: { (snapshot) in
        self.items = []
        for child in snapshot.children.allObjects as! [FIRDataSnapshot] {
            if let dictionary = child.value as? [String: AnyObject] {
                // Create item and append it to an items array
            }
        }
        self.tableView.reloadData()
    })
}

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)                
    self.fetchItems()
}

override func viewDidDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)
    ref.removeAllObservers()
}

Firebase work asynchronously, so instead of calling data in viewWillAppear use a delegate in viewController2 for tableView of viewController1 to reload data. — Basir Alam

Jaime Alcántara Arnela Jaime Alcántara Arnela · Accepted Answer · 2017-04-04T10:52:10

You shouldn't use observeSingleEvent since you want the code to be executed every time the firebase database changes. So, change it:

func fetchItems() {
ref.child("items").observe(.value, with: { (snapshot) in
    self.items = []
    for child in snapshot.children.allObjects as! [FIRDataSnapshot] {
        if let dictionary = child.value as? [String: AnyObject] {
            // Create item and append it to an items array
        }
    }
    self.tableView.reloadData()
})

}

This will create a listener. Also, since you didn't create an observer before, you didn't have to use removeAllObservers(). Now that you have one it's correct to use it. Hope it helps!

Cannot retrieve recently added values with Firebase

1 Answers