iOS Firebase asynchronous data retrieval into Array

Question

I try to retrieve data from Firebase into Array. Because it runs asynchronously, the results that I want to show in my CollectionView is a delay until I switch back and forth. I am very new to asynchronous functions in iOS. Please help me to complete my code.

    ref = Database.database().reference(withPath: "MyTest/Video")
        ref?.observeSingleEvent(of: .value, with: { snapshot in

            if !snapshot.exists() { return }

            if let result = snapshot.children.allObjects as? [DataSnapshot] {
                for child in result {
                    let autoID = child.key as String //get autoID

                    let title = snapshot.childSnapshot(forPath: "\(autoID)/Title").value
                    let url = snapshot.childSnapshot(forPath: "\(autoID)/URL").value
                    let views = snapshot.childSnapshot(forPath: "\(autoID)/Views").value

                    self.arrayAllTitle.append(title as! String)
                    self.arrayAllId.append(url as! String)
                    self.arrayAllDesc.append(views as! String)
                }
            }


        })

You aren't actually calling reloadData() on your collection view once all values have been fetched from Firebase. After the for child in result{...} loop, you should do collectionView.reloadData(). — David Pasztor
– David Pasztor, Commented May 16, 2018 at 18:44

marc_s · Accepted Answer · 2018-05-26 17:24:48Z

1

You need to reload the collection after you retrieve the data so after the for loop call reloadData()

for child in result {

}

self.collectionView.reloadData()

//

func getValueFromDatabase(completion: @escaping (_ status: Bool) -> Void){

    ref = Database.database().reference(withPath: "MyTest/Video")
    ref?.observeSingleEvent(of: .value, with: { snapshot in

        if !snapshot.exists() { return }

        if let result = snapshot.children.allObjects as? [DataSnapshot] {
            for child in result {
                let autoID = child.key as String //get autoID

                let title = snapshot.childSnapshot(forPath: "\(autoID)/Title").value
                let url = snapshot.childSnapshot(forPath: "\(autoID)/URL").value
                let views = snapshot.childSnapshot(forPath: "\(autoID)/Views").value

                self.arrayAllTitle.append(title as! String)
                self.arrayAllId.append(url as! String)
                self.arrayAllDesc.append(views as! String)
            }

            completion(true)
        }
        else {
            completion(false)
        }
    })
}

//

self.getValueFromDatabase { (status) in

    if status {
       // success 
    }
 }

edited May 26, 2018 at 17:24

marc_s

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answered May 16, 2018 at 18:44

Shehata Gamal

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5 Comments

Self_Learner Over a year ago

How can we add "completion"? I read through many problems and it seems like they can use this approach. However, I'm not sure how to apply in within my code. I spent 2 days already fixing this problem. I would appreciate your help pls.

Self_Learner Over a year ago

print works perfectly, but the collectionView still not showing anything.

Shehata Gamal Over a year ago

did you set self.collectionView.dataSource = self

Self_Learner Over a year ago

In viewDidLoad(), I call that function to add values into Arrays. However, collectionView only show results when I click back and forth.

Self_Learner Over a year ago

Thanks a lot. Finally I fix my problem. You made it clear, but I couldn't figure it out at first, lolz..

Elena · Accepted Answer · 2018-05-16 19:34:16Z

0

I'm working with Firebase in my project right now. I would suggest the following solution: wrap the database observer in a distinct function which gets completion block as a parameter.

func getValueFromDatabase(completion: ()->Void){

    ref = Database.database().reference(withPath: "MyTest/Video")
    ref?.observeSingleEvent(of: .value, with: { snapshot in

        if !snapshot.exists() { return }

        if let result = snapshot.children.allObjects as? [DataSnapshot] {
            for child in result {
                let autoID = child.key as String //get autoID

                let title = snapshot.childSnapshot(forPath: "\(autoID)/Title").value
                let url = snapshot.childSnapshot(forPath: "\(autoID)/URL").value
                let views = snapshot.childSnapshot(forPath: "\(autoID)/Views").value

                self.arrayAllTitle.append(title as! String)
                self.arrayAllId.append(url as! String)
                self.arrayAllDesc.append(views as! String)
            }

            completion()
        }
    })
}

This way you can call the function from anywhere providing the desired action after fetching data from db is finished:

getValueFromDatabase(completion:{

    self.collectionView.reloadData() //or any other action you want to fulfil

})

answered May 16, 2018 at 19:34

Elena

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2 Comments

Self_Learner Over a year ago

I followed your approach. I create that function and call it in viewDidLoad() because I want to paste values into Arrays at the first time the app has loaded. It seems doesn't work. Did I do it right?

Self_Learner Over a year ago

I fixed my problem and my code is working now. Thanks a lot :)

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