CODEWITHSUNDEEP
iosswift
kidCoder
kidCoder

Reputation: 354

Simple completion handler or callback in swift

I have the following code, which requests a few JSON objects, and then calls a function to fetch images from a server based off those tags. I am refactoring my code to not force my UICollectionView to reload when the request is complete, so I simply want to collect the images when a user triggers the prior view's tableview segue. In prepareForSegue(), I have the following code:

let priority = DISPATCH_QUEUE_PRIORITY_BACKGROUND
            dispatch_async(dispatch_get_global_queue(priority, 0)) {

                self.performTagRequest(tagText!)
                self.imageRequestCompletionBool = self.requestImages(self.tagResultObject)

            }    
            (segue.destinationViewController as PhotoViewController).detailItem = globalImageArray

How would I go about having the requestImages() function only call once the performTagRequest() function completes, and only then have the detail item set?

I just want to avoid a race on larger calls.

the code for performTagRequest is 

func performTagRequest(detail : String) {
    var request = HTTPTask()
    var formattedDetail = detail.stringByReplacingOccurrencesOfString("\"", withString: "", options: NSStringCompareOptions.LiteralSearch, range: nil)
    var url = "http://www.gifbase.com/tag/\(formattedDetail)?format=json"
    url = url.stringByAddingPercentEscapesUsingEncoding(NSUTF8StringEncoding)!
    request.GET(url, parameters: nil, success: {(response: HTTPResponse) in
        if response.responseObject != nil {
            let data = response.responseObject as NSData
            var tagResponse = TagResponse(JSONDecoder(data)) //Json Object of all image url
            self.tagResultObject = tagResponse
        }
        },failure: {(error: (NSError, HTTPResponse?)) in
            println("error: \(error)")
    })

}

Upvotes: 1

Views: 3293

Answers (1)

nanothread
nanothread

Reputation: 908

Looks like you need a completion handler. Change the declaration of performTagRequest() to something like:

func performTagRequest(tagText: String!, completion: (() -> Void)!)

And to the end of performTagRequest() add:

completion()

To run the completion code.

Then call it like this:

self.performTagRequest(tagText!){
    self.imageRequestCompletionBool = self.requestImages(self.tagResultObject)
}

The above uses trailing closures for simplicity, but you could call it like this:

self.performTagRequest(tagText!, completion:{
            self.imageRequestCompletionBool = self.requestImages(self.tagResultObject)
})

If you want to add other parameters after it.

Upvotes: 6

Related Questions