Fetching CKAsset Image From CloudKit is Very Slow

Question

I am using CloudKit as a server backend for my iOS application. I\'m using it to house some relatively static data along with a handful of images(CKAsset). I ran into a problem

Answer 1

There seems to be something slowing down your main thread which introduces a delay in executing the capture block of your dispatch_async call. Is it possible that your code calls this record fetching function multiple times in parallel ? This would cause the NSData(contentsOfURL: asset.fileURL) processing to hog the main thread and introduce cumulative delays.

In any case, if only as a good practice, loading the image with NSData should be performed in the background and not on the main thread.

Answer 2

I am using CKQueryOperation. I found that once I added the following line to my code that downloading CKAssets sped up by about a factor of 5-10x.

    queryOperation.qualityOfService = .UserInteractive

Here is my full code:

func getReportPhotos(report:Report, completionHandler: (report:Report?, error:NSError?) -> ()) {
    let photo : Photo = report.photos![0] as! Photo
    let predicate : NSPredicate = NSPredicate(format: "recordID = %@", CKRecordID(recordName: photo.identifier!))
    let query : CKQuery = CKQuery(recordType: "Photo", predicate: predicate)
    let queryOperation : CKQueryOperation = CKQueryOperation()
    queryOperation.query = query
    queryOperation.resultsLimit = numberOfReportsPerQuery        
    queryOperation.qualityOfService = .UserInteractive
    queryOperation.recordFetchedBlock = { record in
        photo.date = record.objectForKey("date") as? NSDate
        photo.fileType = record.objectForKey("fileType") as? String
        let asset : CKAsset? = record.objectForKey("image") as? CKAsset
        if asset != nil {
            let photoData : NSData? = NSData(contentsOfURL:asset!.fileURL)
            let photo : Photo = report.photos![0] as! Photo
            photo.image = UIImage(data:photoData!)
        }

    }
    queryOperation.queryCompletionBlock = { queryCursor, error in
        dispatch_async(dispatch_get_main_queue(), {
            completionHandler(report: report, error: error)
        })
    }
    publicDatabase?.addOperation(queryOperation)
}