Why does this loop execute before this piece of code?

Question

Why does the for loop execute before the firebase code even though it is typed in after the firebase code?

messageDB.observe(.childAdded) { (snapshot) in
    let snapshotValue = snapshot.value as! Dictionary<String,String>
    print("Snapshot value \(snapshotValue)")
    let email = snapshotValue["UserEmail"]!
    if (email == Auth.auth().currentUser?.email as String?){
        let user : UserString = UserString()
        user.name = snapshotValue["UserName"]!
        user.height = snapshotValue["UserHeight"]!
        user.weight = snapshotValue["UserWeight"]!
        user.date = snapshotValue["EntryDate"]!
        userArray.append(user)
    }    
}

for index in 0...4{
    print(index)
}

Firstly read [here](https://stackoverflow.com/questions/748175/asynchronous-vs-synchronous-execution-what-does-it-really-mean). Then the observe works async so if you want that the loop is executed after the observe you need to add it into the block. — Kerberos, Aug 01 '19 at 07:14
@Kerberos Thank you! Sorry but I'm really new to iOS development. How can I add the loop into the block so its executed after? — Vishaal Kumar, Aug 01 '19 at 07:26
@VishaalKumar I added an answer because it did not fit into the comment. — Kerberos, Aug 01 '19 at 09:29

score 1 · Answer 1 · answered Aug 01 '19 at 09:24

This is because the firebase observe event is asynchronous, so if you want to execute a code after this you need to move it into the block.

So your code will be:

messageDB.observe(.childAdded) { (snapshot) in
        let snapshotValue = snapshot.value as! Dictionary<String,String>
        print("Snapshot value \(snapshotValue)")
        let email = snapshotValue["UserEmail"]!
        if (email == Auth.auth().currentUser?.email as String?){
            let user : UserString = UserString()
            user.name = snapshotValue["UserName"]!
            user.height = snapshotValue["UserHeight"]!
            user.weight = snapshotValue["UserWeight"]!
            user.date = snapshotValue["EntryDate"]!
            userArray.append(user)
        }
        for index in 0...4{
           print(index)
        }
        // self.afterBlock()
    }

// func afterBlock() { yourCodeHere }

Or call it in a separate method like in the commented code.

Not forget to remove the observe when you dismiss your ViewController.

Why does this loop execute before this piece of code?

1 Answers1