Added a delegate for the web image prefetched.

SDWebImage/SDWebImagePrefetcher.h

@@ -9,6 +9,33 @@
 #import <Foundation/Foundation.h>
 #import "SDWebImageManager.h"
 
+@class SDWebImagePrefetcher;
+
+@protocol SDWebImagePrefetcherDelegate <NSObject>
+
+@optional
+
+/**
+ * Called when an image was prefetched.
+ *
+ * @param imagePrefetcher The current image prefetcher
+ * @param imageURL The image url that was prefetched
+ * @param finishedCount The total number of images that were prefetched
+ * @param totalCount The total number of images that need to be prefetched
+ */
+- (void)imagePrefetcher:(SDWebImagePrefetcher*)imagePrefetcher didPrefetchURL:(NSURL*)imageURL finishedCount:(NSUInteger)finishedCount totalCount:(NSUInteger)totalCount;
+
+/**
+ * Called when all images are prefetched.
+ * @param imagePrefetcher The current image prefetcher
+ * @param totalCount The total number of images that need to be prefetched
+ * @param skippedCount The total number of images that were skipped
+ */
+- (void)imagePrefetcher:(SDWebImagePrefetcher*)imagePrefetcher didFinishWithTotalCount:(NSUInteger)totalCount skippedCount:(NSUInteger)skippedCount;
+
+@end
+
+
 /**
  * Prefetch some URLs in the cache for future use. Images are downloaded in low priority.
  */
@@ -24,6 +51,7 @@
  */
 @property (nonatomic, assign) SDWebImageOptions options;
 
+@property (weak, nonatomic) id<SDWebImagePrefetcherDelegate> delegate;
 
 /**
  * Return the global image prefetcher instance.

SDWebImage/SDWebImagePrefetcher.m

@@ -76,6 +76,13 @@
             // Add last failed
             self.skippedCount++;
         }
+        if ([self.delegate respondsToSelector:@selector(imagePrefetcher:didPrefetchURL:finishedCount:totalCount:)]) {
+            [self.delegate imagePrefetcher:self
+                            didPrefetchURL:self.prefetchURLs[index]
+                             finishedCount:self.finishedCount
+                                totalCount:self.prefetchURLs.count
+             ];
+        }
 
         if (self.prefetchURLs.count > self.requestedCount)
         {
@@ -95,10 +102,16 @@
 
 - (void)reportStatus
 {
-#ifdef SD_VERBOSE
     NSUInteger total = [self.prefetchURLs count];
+#ifdef SD_VERBOSE
     NSLog(@"Finished prefetching (%d successful, %d skipped, timeElasped %.2f)", total - self.skippedCount, self.skippedCount, CFAbsoluteTimeGetCurrent() - self.startedTime);
 #endif
+    if ([self.delegate respondsToSelector:@selector(imagePrefetcher:didFinishWithTotalCount:skippedCount:)]) {
+        [self.delegate imagePrefetcher:self
+               didFinishWithTotalCount:(total - self.skippedCount)
+                          skippedCount:self.skippedCount
+         ];
+    }
 }
 
 - (void)prefetchURLs:(NSArray *)urls