Parse - Asynchronous Block Call - ios

Question

I have the following code that checks if username is taken or not in Parse database. The only problem is that the code is executing and execution continues to next code and then returns the result of this block.
This is leading to a problem with a check I have afterwards on true/false value.
How can I execute the same code below and wait for it to get a result. and based on that, proceed?
let query = PFQuery(className:"User")
query.whereKey("appUsername", equalTo:username)
query.findObjectsInBackgroundWithBlock {
(objects: [PFObject]?, error: NSError?) -> Void in
print("test username: " + username);
if error == nil {
// The find succeeded.
usernameTaken = true;
} else {
// Log details of the failure
usernameTaken = false;
}
}

Answer 1

You know, the PFQuery class, and the whole Parse library, has a detailed documentation. It should have taken you no more than 5 seconds to find that next to the findObjectsInBackgroundWithBlock, there's a findObjects: method that will return the data directly:
https://parse.com/docs/ios/api/Classes/PFQuery.html#//api/name/findObjects
It is however generally a very bad idea to use synchronous requests, especially from the main thread, as this will cause your UI to freeze while the request is made (which is usually quick, but can take a lot longer if the network connection is slow or unreliable). You would be a lot better of extending the completion block paradigm to your own code to propagate the request.

Answer 2

First of all check this: https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Closures.html#//apple_ref/doc/uid/TP40014097-CH11-ID94 to better understand how it's works
You can use some completion block in function that include your code like this:
func result(completion block: (result: Bool) -> Void) {
let query = PFQuery(className:"User")
query.whereKey("appUsername", equalTo:username)
query.findObjectsInBackgroundWithBlock {
(objects: [PFObject]?, error: NSError?) -> Void in
print("test username: " + username);
if error == nil {
// retun true with completion block
block(result: true)
} else {
// return false with completion block
block(result: false)
}
}
}
And you can use it like this:
...
result(completion: {(result: Bool) in
// Here code that use result from your query
...
})
...
Or you can call some your function from findObjectsInBackgroundWithBlock that will use result from query:
func someFunc(result: Bool) {
// Here code that use result from your query
...
}
...
let query = PFQuery(className:"User")
query.whereKey("appUsername", equalTo:username)
query.findObjectsInBackgroundWithBlock {
(objects: [PFObject]?, error: NSError?) -> Void in
print("test username: " + username);
if error == nil {
self.someFunc(true)
} else {
self.someFunc(false)
}
}

Answer 3

Ok so I fixed the execution but placing the check of the boolean variable usernameTaken in the if condition. Things worked after that.