fix image caching at coupon cell

@@ -16,6 +16,24 @@ import UIKit
     @IBOutlet weak var dicountLabel: UILabel!
     @IBOutlet weak var discriptionLabel: UILabel!
     @IBOutlet weak var expirationLabel: UILabel!
+
+    var postImageURL: String? {
+        didSet {
+            if let url = postImageURL {
+                self.couponImage.image = UIImage() // UIImage(named: "loading")
+
+                UIImage.loadImageUsingCacheWithUrlString(url) { image in
+                    // set the image only when we are still displaying the content for the image we finished downloading
+                    if url == self.postImageURL {
+                        self.couponImage.image = image
+                    }
+                }
+            }
+            else {
+                self.couponImage.image = nil
+            }
+        }
+    }
     
     
     public override func awakeFromNib() {
@@ -54,7 +72,8 @@ import UIKit
         
         for merchant in merchantList {
             if (merchant._uuid == couponSetData?.merchant_uuid) {
-                couponImage.load(link: merchant._img_preview, placeholder: UIImage(), cache: URLCache())
+                // couponImage.load(link: merchant._img_preview, placeholder: UIImage(), cache: URLCache())
+                self.postImageURL = merchant._img_preview
                 nameLabel.text = merchant._admin_name
                 break;
             }