Setting label text after completing block Swift

Question

I want to set user name to a label because my block ("findObjectsInBackgroundWithBlock") is taking time to complete and label.text sets nil .

how to set label text after completing the block??

class test {         

var userName: String? // variable to access user name returned by block        
private func loadData() {      

getCurrentUser()         
lblUserName.text = userName       

}    

}

This is the block where i am getting user data from Parse.

private func getCurrentUser() {         

        if PFUser.currentUser() != nil { 

            currentUser = PFUser.currentUser()?.username    
            let query = PFQuery(className: "_User")    
            query.whereKey("username", equalTo: currentUser!)    
            query.findObjectsInBackgroundWithBlock { (currentUsers, error) -> Void in 
                if error == nil {     
                    for user in currentUsers! {     
                       userName = user["name"] as? String      
                    }   
                }
            }
        }
    }

Answer 1

You can use a property observer here like this:

var userName: String? {
    didset {
       if let name = username {
           lblUserName.text = name
       } 
    }
}

Answer 2

You can add a completion handler function argument to your getCurrentUser function and call that handler when you retrived the data:

private func getCurrentUser(completion: (result: String) -> Void) {         
    if PFUser.currentUser() != nil { 
        currentUser = PFUser.currentUser()?.username    
        let query = PFQuery(className: "_User")    
        query.whereKey("username", equalTo: currentUser!)    
        query.findObjectsInBackgroundWithBlock { (currentUsers, error) -> Void in 
            if error == nil {     
                for user in currentUsers! {     
                   completion(user["name"] as? String)     
                }   
            }
        }
    }
}

Then pass the complition function like this:

getCurrentUser() { (result: String) in
    self.lblUserName.text = result
}  

I cannot prove it is fully working code as I don't have XCode now to test it. But you should get the idea.