fix race condition when use transition

SDWebImage/Core/UIView+WebCache.h

@@ -34,6 +34,7 @@ typedef void(^SDSetImageBlock)(UIImage * _Nullable image, NSData * _Nullable ima
 /**
  * Get the current image operation key. Operation key is used to identify the different queries for one view instance (like UIButton).
  * See more about this in `SDWebImageContextSetImageOperationKey`.
+ * If you cancel current image load, the key will be set to nil.
  * @note You can use method `UIView+WebCacheOperation` to investigate different queries' operation.
  */
 @property (nonatomic, strong, readonly, nullable) NSString *sd_latestOperationKey;

SDWebImage/Core/UIView+WebCache.m

@@ -203,6 +203,7 @@ const int64_t SDWebImageProgressUnitCountUnknown = 1LL;
 
 - (void)sd_cancelCurrentImageLoad {
     [self sd_cancelImageLoadOperationWithKey:self.sd_latestOperationKey];
+    self.sd_latestOperationKey = nil;
 }
 
 - (void)sd_setImage:(UIImage *)image imageData:(NSData *)imageData basedOnClassOrViaCustomSetImageBlock:(SDSetImageBlock)setImageBlock cacheType:(SDImageCacheType)cacheType imageURL:(NSURL *)imageURL {
@@ -228,14 +229,18 @@ const int64_t SDWebImageProgressUnitCountUnknown = 1LL;
     } else if ([view isKindOfClass:[UIImageView class]]) {
         UIImageView *imageView = (UIImageView *)view;
         finalSetImageBlock = ^(UIImage *setImage, NSData *setImageData, SDImageCacheType setCacheType, NSURL *setImageURL) {
+            if (view.sd_latestOperationKey != nil) {
                 imageView.image = setImage;
+            }
         };
     }
 #if SD_UIKIT
     else if ([view isKindOfClass:[UIButton class]]) {
         UIButton *button = (UIButton *)view;
         finalSetImageBlock = ^(UIImage *setImage, NSData *setImageData, SDImageCacheType setCacheType, NSURL *setImageURL) {
+            if (view.sd_latestOperationKey != nil) {
                 [button setImage:setImage forState:UIControlStateNormal];
+            }
         };
     }
 #endif
@@ -243,7 +248,9 @@ const int64_t SDWebImageProgressUnitCountUnknown = 1LL;
     else if ([view isKindOfClass:[NSButton class]]) {
         NSButton *button = (NSButton *)view;
         finalSetImageBlock = ^(UIImage *setImage, NSData *setImageData, SDImageCacheType setCacheType, NSURL *setImageURL) {
+            if (view.sd_latestOperationKey != nil) {
                 button.image = setImage;
+            }
         };
     }
 #endif

Tests/Tests/SDWebCacheCategoriesTests.m

@@ -208,6 +208,7 @@
     [imageView sd_internalSetImageWithURL:originalImageURL placeholderImage:nil options:0 context:nil setImageBlock:nil progress:nil completed:nil];
     [imageView sd_cancelCurrentImageLoad];
     NSString *operationKey = NSStringFromClass(UIView.class);
+    expect(imageView.sd_latestOperationKey).beNil();
     expect([imageView sd_imageLoadOperationForKey:operationKey]).beNil();
 }