Adding a completion block to a CloudKit function - swift

Question

My ViewController wants to display some data based on a CloudKit query.
My CloudKit code is all in a separate class. That class has a function called loadExpenses() that fetches some Expenses entities from CK.
I want to be able to call loadExpenses() from the VC, so I need a completion block provided by the function to update the UI from the VC.
This is what loadExpenses() looks like:
func loadExpenses() {
let pred = NSPredicate(value: true)
let sort = NSSortDescriptor(key: "creationDate", ascending: true)
let query = CKQuery(recordType: "Expense", predicate: pred)
query.sortDescriptors = [sort]
let operation = CKQueryOperation(query: query)
operation.desiredKeys = ["person", "action", "amount", "timestamp"]
operation.resultsLimit = 50
var newExpenses = [Expense]()
operation.recordFetchedBlock = { (record) in
let recordID = record.recordID
let person = record["person"] as! String
let action = record["action"] as! String
let amount = record["amount"] as! Double
let timestamp = record["timestamp"] as! NSDate
let expense = Expense(person: person, action: action, amount: amount, timestamp: timestamp)
newExpenses.append(expense)
}
// This is the part that needs to be changed
operation.queryCompletionBlock = { [unowned self] (cursor, error) in
dispatch_async(dispatch_get_main_queue()) {
if error == nil {
self.objects = newExpenses
self.tableView.reloadData()
self.refreshRealmDataFromCK()
} else {
let ac = UIAlertController(title: "Fetch failed", message: "There was a problem fetching the list of expenses; please try again: \(error!.localizedDescription)", preferredStyle: .Alert)
ac.addAction(UIAlertAction(title: "OK", style: .Default, handler: nil))
self.presentViewController(ac, animated: true, completion: nil)
}
}
}
CKContainer.defaultContainer().privateCloudDatabase.addOperation(operation)
}
Obviously the last part won't execute, considering all those self.property belong to the VC (I kept them just to show what I need to do in the VC).
As I said, I want to be able to call this function from the VC and get/use a completion block to update those properties. How do I do that?

Answer 1

You need to pass a block as a parameter to the loadExpenses() function. So it should actually be defined something like loadExpenses(completionBlock:([whatever parameters you need in here])->Void).
Then, you can call the passed completionBlock block (with appropriate parameters) from within the operation.queryCompletionBlock block.
EDIT:
So this is not tested at all of course, but you could give it a shot:
func loadExpenses(completionBlock:([Expense])->Void) {
let pred = NSPredicate(value: true)
let sort = NSSortDescriptor(key: "creationDate", ascending: true)
let query = CKQuery(recordType: "Expense", predicate: pred)
query.sortDescriptors = [sort]
let operation = CKQueryOperation(query: query)
operation.desiredKeys = ["person", "action", "amount", "timestamp"]
operation.resultsLimit = 50
var newExpenses = [Expense]()
operation.recordFetchedBlock = { (record) in
let recordID = record.recordID
let person = record["person"] as! String
let action = record["action"] as! String
let amount = record["amount"] as! Double
let timestamp = record["timestamp"] as! NSDate
let expense = Expense(person: person, action: action, amount: amount, timestamp: timestamp)
newExpenses.append(expense)
}
// This is the part that needs to be changed
operation.queryCompletionBlock = { [unowned self] (cursor, error) in
completionBlock(newExpenses)
}
CKContainer.defaultContainer().privateCloudDatabase.addOperation(operation)
}
And then call it like this:
loadExpenses({ (newExpenses:[Expense]) -> Void in {
dispatch_async(dispatch_get_main_queue()) {
if error == nil {
self.objects = newExpenses
self.tableView.reloadData()
self.refreshRealmDataFromCK()
} else {
let ac = UIAlertController(title: "Fetch failed", message: "There was a problem fetching the list of expenses; please try again: \(error!.localizedDescription)", preferredStyle: .Alert)
ac.addAction(UIAlertAction(title: "OK", style: .Default, handler: nil))
self.presentViewController(ac, animated: true, completion: nil)
}
}
}