Do not init an activity indictor if image isn't downloading in demo app (good practice)

Author: Olivier Poitrey

Examples/SDWebImage Demo/DetailViewController.m

@@ -33,13 +33,20 @@ - (void)configureView
 {
     if (self.imageURL)
     {
-        UIActivityIndicatorView *activityIndicator;
-        [self.imageView addSubview:activityIndicator = [UIActivityIndicatorView.alloc initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray]];
-        activityIndicator.center = self.imageView.center;
-        [activityIndicator startAnimating];
-        [self.imageView setImageWithURL:self.imageURL placeholderImage:nil options:SDWebImageProgressiveDownload completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType)
+        __block UIActivityIndicatorView *activityIndicator;
+        [self.imageView setImageWithURL:self.imageURL placeholderImage:nil options:SDWebImageProgressiveDownload progress:^(NSUInteger receivedSize, long long expectedSize)
+        {
+            if (!activityIndicator)
+            {
+                [self.imageView addSubview:activityIndicator = [UIActivityIndicatorView.alloc initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray]];
+                activityIndicator.center = self.imageView.center;
+                [activityIndicator startAnimating];
+            }
+        }
+        completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType)
         {
             [activityIndicator removeFromSuperview];
+            activityIndicator = nil;
         }];
     }
 }