Loads image from URL

UIImage+loadFromURL.swift

//
//  UIImage+loadFromURL.swift
//
//  Created by Artem Krachulov
//  Copyright (c) 2016 Artem Krachulov. All rights reserved.
//	http://www.artemkrachulov.com
//

import UIKit

extension UIImage {
  
  /// Loads image from URL. When load finished will execute block object.  This block has no return value and takes a single UIImage argument that replesent loaded image in UIImage object
  ///
  /// Usage:
  ///
  ///		var imageView = UIImageView(frame: CGRectMake(0, 0, 500, 500))
  ///
  ///		UIImage.loadFromURL("__URL__",
  ///		  completion: { (image) -> () in
  ///		    imageView.image = image
  ///		  }
  ///		)
  public class func loadFromURL(url: String, completion: (UIImage)->()) -> UIImage? {
    
    guard !url.isEmpty else {
      return nil
    }
    
    guard let url = NSURL(string: url) else {
      return nil
    }
    
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), {
      if let data = NSData(contentsOfURL: url) {
        
        dispatch_async(dispatch_get_main_queue(), {
          if let image = UIImage(data: data) {
            
            completion(image)
          }
        })
      }
    })
    
    return nil
  }
}