iPhone SDK Application Development

Chapter 5. Layer Programming with Quartz Core

The Quartz Core framework is referred to as Core Animation on the Leopard desktop. Quartz Core provides the underlying classes for managing the layers of UIView objects. It is also used to create 3D transformations of 2D objects for stunning animations and effects.

To use the Quartz Core framework, you’ll need to add it to your Xcode project. Right-click on the Frameworks folder in your project, and then choose Add Framework. Navigate to the QuartzCore.framework folder, and then click Add.

Warning

To find the Quartz Core framework, you may have to navigate manually into either /Developer/Platforms/iPhoneOS.platform or /Developer/Platforms/iPhoneSimulator.platform and locate the Frameworks folder in your SDK.

Understanding Layers

A layer is a low-level component found in displayable classes. Layers act like a sheet of poster board to which an object’s contents are affixed. It acts as a flexible backing for the object’s display contents and can bend or contort the content in many ways on the screen. Every object that is capable of rendering itself—namely, those derived from the UIView class—has a layer to which its contents are glued.

For example, the UIImageView class contains all the basic information about a two-dimensional image—its display region, resolution, and various methods for working with and rendering the image. The image itself is glued to the parent UIView class’s layer, which is like the backing in a picture frame. The most basic ...