Remove some unused code, fix typo, update the comments

SDWebImage/UIButton+WebCache.m

@@ -146,18 +146,10 @@ static inline NSString * backgroundImageURLKeyForState(UIControlState state) {
                            completed:completedBlock];
 }
 
-- (void)sd_setImageLoadOperation:(id<SDWebImageOperation>)operation forState:(UIControlState)state {
-    [self sd_setImageLoadOperation:operation forKey:[NSString stringWithFormat:@"UIButtonImageOperation%@", @(state)]];
-}
-
 - (void)sd_cancelImageLoadForState:(UIControlState)state {
     [self sd_cancelImageLoadOperationWithKey:[NSString stringWithFormat:@"UIButtonImageOperation%@", @(state)]];
 }
 
-- (void)sd_setBackgroundImageLoadOperation:(id<SDWebImageOperation>)operation forState:(UIControlState)state {
-    [self sd_setImageLoadOperation:operation forKey:[NSString stringWithFormat:@"UIButtonBackgroundImageOperation%@", @(state)]];
-}
-
 - (void)sd_cancelBackgroundImageLoadForState:(UIControlState)state {
     [self sd_cancelImageLoadOperationWithKey:[NSString stringWithFormat:@"UIButtonBackgroundImageOperation%@", @(state)]];
 }

SDWebImage/UIImageView+WebCache.m

@@ -109,18 +109,18 @@
     }];
 }
 
-static char animationloadOperationKey;
+static char animationLoadOperationKey;
 
 // element is weak because operation instance is retained by SDWebImageManager's runningOperations property
 // we should use lock to keep thread-safe because these method may not be acessed from main queue
 - (NSPointerArray *)sd_animationOperationArray {
     @synchronized(self) {
-        NSPointerArray *operationsArray = objc_getAssociatedObject(self, &animationloadOperationKey);
+        NSPointerArray *operationsArray = objc_getAssociatedObject(self, &animationLoadOperationKey);
         if (operationsArray) {
             return operationsArray;
         }
         operationsArray = [NSPointerArray weakObjectsPointerArray];
-        objc_setAssociatedObject(self, &animationloadOperationKey, operationsArray, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
+        objc_setAssociatedObject(self, &animationLoadOperationKey, operationsArray, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
         return operationsArray;
     }
 }

SDWebImage/UIView+WebCacheOperation.h

@@ -12,10 +12,12 @@
 
 #import "SDWebImageManager.h"
 
+// These methods are used to support canceling for UIView image loading, it's designed to be used internal but not external.
+// All the stored operations are weak, so it will be dalloced after image loading finished. If you need to store operations, use your own class to keep a strong reference for them.
 @interface UIView (WebCacheOperation)
 
 /**
- *  Set the image load operation (storage in a UIView based dictionary)
+ *  Set the image load operation (storage in a UIView based weak map table)
  *
  *  @param operation the operation
  *  @param key       key for storing the operation

SDWebImage/UIView+WebCacheOperation.m

@@ -16,7 +16,7 @@ static char loadOperationKey;
 
 // key is copy, value is weak because operation instance is retained by SDWebImageManager's runningOperations property
 // we should use lock to keep thread-safe because these method may not be acessed from main queue
-typedef NSMapTable<NSString *, id> SDOperationsDictionary;
+typedef NSMapTable<NSString *, id<SDWebImageOperation>> SDOperationsDictionary;
 
 @implementation UIView (WebCacheOperation)
 
@@ -47,13 +47,13 @@ typedef NSMapTable<NSString *, id> SDOperationsDictionary;
 - (void)sd_cancelImageLoadOperationWithKey:(nullable NSString *)key {
     // Cancel in progress downloader from queue
     SDOperationsDictionary *operationDictionary = [self sd_operationDictionary];
-    id operation;
+    id<SDWebImageOperation> operation;
     @synchronized (self) {
         operation = [operationDictionary objectForKey:key];
     }
     if (operation) {
         if ([operation conformsToProtocol:@protocol(SDWebImageOperation)]){
-            [(id<SDWebImageOperation>) operation cancel];
+            [operation cancel];
         }
         @synchronized (self) {
             [operationDictionary removeObjectForKey:key];