Programming iOS 6, 3rd Edition

Exploring the Music Library

Everything in the music library, as seen by your code, is an MPMediaEntity. This is an abstract class that endows its subclasses with the ability to describe themselves through key–value pairs called properties. (This use of the word “properties” has nothing to do with the Objective-C properties discussed in Chapter 12; these properties are more like entries in an NSDictionary.) The repertoire of properties depends on the sort of entity you’re looking at; many of them will be intuitively familiar from your use of iTunes. For example, a media item has a title, an album title, a track number, an artist, a composer, and so on; a playlist has a title, a flag indicating whether it is a “smart” playlist, and so on. The property keys have names like MPMediaItemPropertyTitle.

To fetch a property’s value, call valueForProperty: with its key. You can fetch multiple properties with enumerateValuesForProperties:usingBlock:.

An individual item in the music library is an MPMediaItem, an MPMediaEntity subclass. It has a type, according to the value of its MPMediaItemPropertyMediaType property: it might, for example, be music, a podcast, an audiobook, or a video. Different types of item have slightly different properties; for example, a podcast, in addition to its normal title, has a podcast title.

An item’s artwork image is an instance of the MPMediaItemArtwork class, from which you are supposed to be able to get the image itself scaled to a specified size by calling ...