Start downloading images when multiplex node is displayed

fixes #178

AsyncDisplayKit/ASMultiplexImageNode.mm

@@ -70,7 +70,6 @@ typedef void(^ASMultiplexImageLoadCompletionBlock)(UIImage *image, id imageIdent
 
   // Networking.
   id _downloadIdentifier;
-  BOOL _canceledImageDownload;
 }
 
 //! @abstract Read-write redeclaration of property declared in ASMultiplexImageNode.h.
@@ -79,16 +78,6 @@ typedef void(^ASMultiplexImageLoadCompletionBlock)(UIImage *image, id imageIdent
 //! @abstract The image identifier that's being loaded by _loadNextImageWithCompletion:.
 @property (nonatomic, readwrite, copy) id loadingImageIdentifier;
 
-/**
-  @abstract Indicates whether a change from one array of image identifiers to another should prompt the receiver to update its loaded image.
-  @param loadedIdentifier The image identifier that's currently loaded, or nil if no identifier is loaded yet.
-  @param loadingImageIdentifier The image identifier that's currently loading, or nil if no identifier is loading.
-  @param oldIdentifiers An array of image identifiers that were previously managed, or nil if no identifiers were managed before.
-  @param newIdentifiers The array of new image identifiers.
-  @result YES if the receiver should update its loaded image as a consequence of the newly assigned identifiers; NO otherwise.
- */
-static inline BOOL _shouldUpdateAfterChangedImageIdentifiers(id loadedIdentifier, id loadingImageIdentifier, NSArray *oldIdentifiers, NSArray *newIdentifiers);
-
 /**
   @abstract Returns the next image identifier that should be downloaded.
   @discussion This method obeys and reflects the value of `downloadsIntermediateImages`.
@@ -180,7 +169,6 @@ static inline BOOL _shouldUpdateAfterChangedImageIdentifiers(id loadedIdentifier
   if (_downloadIdentifier) {
     [_downloader cancelImageDownloadForIdentifier:_downloadIdentifier];
     _downloadIdentifier = nil;
-    _canceledImageDownload = YES;
   }
 }
 
@@ -188,10 +176,7 @@ static inline BOOL _shouldUpdateAfterChangedImageIdentifiers(id loadedIdentifier
 {
   [super displayWillStart];
 
-  if(_canceledImageDownload) {
+  [self _loadImageIdentifiers];
-    [self _updatedImageIdentifiers];
-    _canceledImageDownload = NO;
-  }
 }
 
 - (void)displayDidFinish
@@ -268,24 +253,16 @@ static inline BOOL _shouldUpdateAfterChangedImageIdentifiers(id loadedIdentifier
     OSSpinLockUnlock(&_imageIdentifiersLock);
     return;
   }
-
+  
-  NSArray *oldImageIdentifiers = [[NSArray alloc] initWithArray:_imageIdentifiers];
-
   _imageIdentifiers = [imageIdentifiers copy];
-
-  // Kick off image loading and display, if the identifiers have substantively changed.
-  BOOL shouldUpdateAfterChangedImageIdentifiers = _shouldUpdateAfterChangedImageIdentifiers(self.loadedImageIdentifier, self.loadingImageIdentifier, oldImageIdentifiers, _imageIdentifiers);
-
   OSSpinLockUnlock(&_imageIdentifiersLock);
-
-  if (shouldUpdateAfterChangedImageIdentifiers) {
-    [self _updatedImageIdentifiers];
-  }
 }
 
 - (void)reloadImageIdentifierSources
 {
-  [self _updatedImageIdentifiers];
+  // setting this to nil makes the node think it has not downloaded any images
+  _loadedImageIdentifier = nil;
+  [self _loadImageIdentifiers];
 }
 
 #pragma mark -
@@ -325,18 +302,10 @@ static inline BOOL _shouldUpdateAfterChangedImageIdentifiers(id loadedIdentifier
   _downloadIdentifier = downloadIdentifier;
 }
 
+
 #pragma mark - Image Loading Machinery
-static inline BOOL _shouldUpdateAfterChangedImageIdentifiers(id loadedIdentifier, id loadingImageIdentifier, NSArray *oldIdentifiers, NSArray *newIdentifiers)
-{
-  // If we're loading an identifier, we need to update if it isn't permitted to load anymore.
-  if (loadingImageIdentifier)
-    return ![newIdentifiers containsObject:loadingImageIdentifier];
 
-  // We're not loading, so we need to update unless we've already loaded the best identifier.
+- (void)_loadImageIdentifiers
-  return ![[newIdentifiers firstObject] isEqual:loadedIdentifier];
-}
-
-- (void)_updatedImageIdentifiers
 {
   // Kill any in-flight downloads.
   [self _setDownloadIdentifier:nil];

AsyncDisplayKitTests/ASMultiplexImageNodeTests.m

@@ -108,6 +108,7 @@ static BOOL ASRunRunLoopUntilBlockIsTrue(BOOL (^block)())
   [[[mockDataSource expect] andReturn:testImage] multiplexImageNode:imageNode imageForImageIdentifier:imageIdentifier];
 
   imageNode.imageIdentifiers = @[imageIdentifier];
+  [imageNode reloadImageIdentifierSources];
 
   [mockDataSource verify];
 
@@ -153,8 +154,9 @@ static BOOL ASRunRunLoopUntilBlockIsTrue(BOOL (^block)())
     completionBlock([self _testImage].CGImage);
   }] fetchCachedImageWithURL:[OCMArg any] callbackQueue:[OCMArg any] completion:[OCMArg any]];
 
-  // Kick off loading.
   imageNode.imageIdentifiers = @[imageIdentifier];
+  // Kick off loading.
+  [imageNode reloadImageIdentifierSources];
 
   // Verify the data source.
   [mockDataSource verify];
@@ -189,6 +191,7 @@ static BOOL ASRunRunLoopUntilBlockIsTrue(BOOL (^block)())
   }] multiplexImageNode:[OCMArg any] imageForImageIdentifier:[OCMArg any]];
 
   imageNode.imageIdentifiers = @[highResIdentifier];
+  [imageNode reloadImageIdentifierSources];
 
   // At this point, we should have the high-res identifier loaded and the DS should have been hit once.
   XCTAssertEqualObjects(imageNode.loadedImageIdentifier, highResIdentifier, @"High res identifier should be loaded.");
@@ -197,10 +200,11 @@ static BOOL ASRunRunLoopUntilBlockIsTrue(BOOL (^block)())
   // Add the low res identifier.
   NSNumber *lowResIdentifier = @1;
   imageNode.imageIdentifiers = @[highResIdentifier, lowResIdentifier];
+  [imageNode reloadImageIdentifierSources];
 
-  // At this point the high-res should still be loaded, and the data source should not have been hit.
+  // At this point the high-res should still be loaded, and the data source should have been hit again
   XCTAssertEqualObjects(imageNode.loadedImageIdentifier, highResIdentifier, @"High res identifier should be loaded.");
-  XCTAssertTrue(dataSourceHits == 1, @"Unexpected DS hit count");
+  XCTAssertTrue(dataSourceHits == 2, @"Unexpected DS hit count");
 
   imageNode.delegate = nil;
   imageNode.dataSource = nil;
@@ -226,6 +230,7 @@ static BOOL ASRunRunLoopUntilBlockIsTrue(BOOL (^block)())
   }] multiplexImageNode:[OCMArg any] imageForImageIdentifier:[OCMArg any]];
 
   imageNode.imageIdentifiers = @[lowResIdentifier];
+  [imageNode reloadImageIdentifierSources];
 
   // At this point, we should have the low-res identifier loaded and the DS should have been hit once.
   XCTAssertEqualObjects(imageNode.loadedImageIdentifier, lowResIdentifier, @"Low res identifier should be loaded.");
@@ -234,6 +239,7 @@ static BOOL ASRunRunLoopUntilBlockIsTrue(BOOL (^block)())
   // Add the low res identifier.
   NSNumber *highResIdentifier = @2;
   imageNode.imageIdentifiers = @[highResIdentifier, lowResIdentifier];
+  [imageNode reloadImageIdentifierSources];
 
   // At this point the high-res should be loaded, and the data source should been hit twice.
   XCTAssertEqualObjects(imageNode.loadedImageIdentifier, highResIdentifier, @"High res identifier should be loaded.");
@@ -282,6 +288,7 @@ static BOOL ASRunRunLoopUntilBlockIsTrue(BOOL (^block)())
   }] multiplexImageNode:[OCMArg any] imageForImageIdentifier:[OCMArg any]];
 
   imageNode.imageIdentifiers = imageIdentifiers;
+  [imageNode reloadImageIdentifierSources];
 
   XCTAssertTrue(loadedImageCount == identifierCount, @"Expected to load the same number of identifiers we supplied");
 
@@ -331,8 +338,9 @@ static BOOL ASRunRunLoopUntilBlockIsTrue(BOOL (^block)())
   [[mockDelegate expect] multiplexImageNode:imageNode didUpdateImage:[OCMArg any] withIdentifier:imageIdentifier fromImage:nil withIdentifier:nil];
   imageNode.delegate = mockDelegate;
 
-  // Kick off loading.
   imageNode.imageIdentifiers = @[imageIdentifier];
+  // Kick off loading.
+  [imageNode reloadImageIdentifierSources];
 
   // Wait until the image is loaded.
   ASRunRunLoopUntilBlockIsTrue(^BOOL{

examples/Multiplex/Sample/ViewController.m

@@ -50,7 +50,7 @@
   _textLabel.font = [UIFont fontWithName:@"HelveticaNeue-Light" size:22.0f];
 
   // tap to reload
-  UITapGestureRecognizer *gr = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(start)];
+  UITapGestureRecognizer *gr = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(reload:)];
   [_textLabel addGestureRecognizer:gr];
 
 
@@ -92,10 +92,14 @@
   _textLabel.text = @"loading…";
   _textLabel.userInteractionEnabled = NO;
 
-  _imageNode.imageIdentifiers = nil;
   _imageNode.imageIdentifiers = @[ @"best", @"medium", @"worst" ]; // go!
 }
 
+- (void)reload:(id)sender {
+  [self start];
+  [_imageNode reloadImageIdentifierSources];
+}
+
 
 #pragma mark -
 #pragma mark ASMultiplexImageNode data source & delegate.