Specialized Layers - iOS Core Animation - page 124

Figure 6.10 The ReflectionView automatically creates a reflection at runtime
A more complete, open source implementation of the ReflectionView class, complete
with an adjustable gradient fade effect (implemented using CAGradientLayer and layer
masking), can be found at https://github.com/nicklockwood/ReflectionView .
CAScrollLayer
For an untransformed layer, the size of a layer's bounds will match the size of its frame .
The frame is calculated automatically from the bounds , so changing either property will
update the other.
But what if you want to display only a small part of a larger layer? For example, you might
have a large image that you want the user to be able to scroll around, or a long list of data
or text. In a typical iOS application, you might use a UITableView or UIScrollView ,
for this, but what's the equivalent when working with standalone layers?
In Chapter 2, we explored the use of the layer contentsRect property, which is a good
solution for displaying only a small part of a larger image in a layer. It's not a very good
solution if your layer contains sublayers, though, as you would need to manually recalculate
and update all the sublayer positions every time you wanted to “scroll” the visible area.
That's where CAScrollLayer comes in. CAScrollLayer has a
-scrollToPoint: method that automatically adjusts the origin of the bounds so that
the layer contents appear to scroll. Note, however, that that is all it does. As discussed
earlier, Core Animation does not handle user input, so CAScrollLayer is not
responsible for turning touch events into a scrolling action, nor does it render scrollbars or