DMScrollViewStack LayoutSubviews

gistfile1.m

- (void) layoutSubviews:(BOOL) aAnimated completion:(void (^)(void)) aCompletion {
	void (^layoutBlock)(void) = ^void(void) {
		static BOOL isScrollView;
		static CGRect visibleRect;
		static CGFloat currentOffset;
		static CGRect idealFrame;
		static CGRect subviewFrame;
		
		visibleRect = CGRectMake(0.0f, self.contentOffset.y, CGRectGetWidth(self.frame), CGRectGetHeight(self.frame));
		currentOffset = 0.0f;
		NSUInteger idx = 0;
		for (UIView *subview in viewsArray) {
			isScrollView = [subview isKindOfClass:[UIScrollView class]];
			// This is the ideal (expanded) frame of the subview
			idealFrame = CGRectMake(0.0f,
									currentOffset,
									self.frame.size.width,
									(isScrollView ? ((UIScrollView*)subview).contentSize.height : [viewsArrayHeight[idx] floatValue]));
			
			subviewFrame = idealFrame;
			if (CGRectIntersectsRect(visibleRect, idealFrame)) { // if subview is visible
				if (isScrollView) {
					CGFloat endOfScrollReachedValue = 0;
					if (CGRectGetMinY(subviewFrame) < self.contentOffset.y) {
						// When the scrollview offset y is behind the current offset of the outer scroll view we
						// set the origin of the scrollview at y=0 and the height to the visible height of the scrollview itself from the outer view
						endOfScrollReachedValue = (self.contentOffset.y+self.frame.size.height - CGRectGetMaxY(idealFrame));
						subviewFrame.origin.y = self.contentOffset.y;
						((UIScrollView*)subview).contentOffset = CGPointMake(0,self.contentOffset.y-idealFrame.origin.y);
					} else {
						// We want to mantain the normal content offset until the table offset y > current visible offset
						((UIScrollView*)subview).contentOffset = CGPointZero;
					}
					
					CGFloat visibleHeight = MIN(self.contentSize.height,MAX(0,self.contentOffset.y+CGRectGetHeight(self.frame)-CGRectGetMinY(subviewFrame)));
					subviewFrame.size.height = visibleHeight-endOfScrollReachedValue;
				}
				// With a simple view frame is the expanded frame (=idealFrame).
				// With a scroll view we set the size of the scroll big enough to fit only the visible dimension
				subview.frame = subviewFrame;
			} else {
				// If subview is invisible we can set it's frame to zero (with tables and collection view we can avoid loading hidden cells)
				subviewFrame = CGRectMake(0, subviewFrame.origin.y, 0, 0);
			}
			++idx;
		}
		self.contentSize = CGSizeMake(CGRectGetWidth(visibleRect),currentOffset);
	};
	
	if (aAnimated)
		[UIView animateWithDuration:0.25f animations:layoutBlock completion:^(BOOL finished) {
			if (aCompletion) aCompletion();
		}];
	else {
		layoutBlock();
		if (aCompletion) aCompletion();
	}
}