[ASVideoNode] Add delegate method called when the currentItem is set.

Author: flovouin

AsyncDisplayKit/ASVideoNode.h

@@ -121,6 +121,12 @@ NS_ASSUME_NONNULL_BEGIN
  * @param videoNode The videoNode
  */
 - (void)videoNodeDidFinishInitialLoading:(ASVideoNode *)videoNode;
+/**
+ * @abstract Delegate method invoked when the AVPlayerItem for the asset has been set up and can be accessed throught currentItem.
+ * @param videoNode The videoNode.
+ * @param currentItem The AVPlayerItem that was constructed from the asset.
+ */
+- (void)videoNode:(ASVideoNode *)videoNode didSetCurrentItem:(AVPlayerItem *)currentItem;
 /**
  * @abstract Delegate method invoked when the video node has recovered from the stall
  * @param videoNode The videoNode

AsyncDisplayKit/ASVideoNode.mm

@@ -46,6 +46,7 @@ @interface ASVideoNode ()
     unsigned int delegateVideoNodeDidPlayToTimeInterval:1;
     unsigned int delegateVideoNodeDidStartInitialLoading:1;
     unsigned int delegateVideoNodeDidFinishInitialLoading:1;
+    unsigned int delegateVideoNodeDidSetCurrentItem:1;
     unsigned int delegateVideoNodeDidStallAtTimeInterval:1;
     unsigned int delegateVideoNodeDidRecoverFromStall:1;
 
@@ -150,7 +151,11 @@ - (void)prepareToPlayAsset:(AVAsset *)asset withKeys:(NSArray<NSString *> *)requ
   } else {
     self.player = [AVPlayer playerWithPlayerItem:playerItem];
   }
-  
+
+  if (_delegateFlags.delegateVideoNodeDidSetCurrentItem) {
+    [_delegate videoNode:self didSetCurrentItem:playerItem];
+  }
+
   if (self.image == nil) {
     [self generatePlaceholderImage];
   }
@@ -464,6 +469,7 @@ - (void)setDelegate:(id<ASVideoNodeDelegate>)delegate
     _delegateFlags.delegateVideoNodeDidPlayToTimeInterval = [_delegate respondsToSelector:@selector(videoNode:didPlayToTimeInterval:)];
     _delegateFlags.delegateVideoNodeDidStartInitialLoading = [_delegate respondsToSelector:@selector(videoNodeDidStartInitialLoading:)];
     _delegateFlags.delegateVideoNodeDidFinishInitialLoading = [_delegate respondsToSelector:@selector(videoNodeDidFinishInitialLoading:)];
+    _delegateFlags.delegateVideoNodeDidSetCurrentItem = [_delegate respondsToSelector:@selector(videoNode:didSetCurrentItem:)];
     _delegateFlags.delegateVideoNodeDidStallAtTimeInterval = [_delegate respondsToSelector:@selector(videoNode:didStallAtTimeInterval:)];
     _delegateFlags.delegateVideoNodeDidRecoverFromStall = [_delegate respondsToSelector:@selector(videoNodeDidRecoverFromStall:)];