Learning Swift

Chapter 13. Extending iOS Apps

In this chapter, we’ll add app extensions to the Notes app. In particular, we’ll be adding a Spotlight indexing extension, which will ensure that all documents are kept up-to-date; and a Today screen extension, which will add an entry to the user’s Notification Center that gives quick access to the user’s documents.

An app extension is a program that’s embedded in an app and used by the system for some auxiliary role. There are many different app extension types available:

• Action extensions appear as entries in a UIActivityController, allowing your app to receive and process content. Dropbox’s “Save to Dropbox” feature is an action extension.

• Audio unit extensions allow an app to provide an audio unit, which is a plug-in that audio-processing apps can use to generate, modify, or receive audio.

• Content blocker extensions allow an app to provide a list of URLs and URL patterns that Safari will refuse to load resources from. Content blockers are primarily designed to let apps provide ad-blocking functionality to Safari by filtering out content from specific sites, such as ads hosted on ad-providing servers.

• Custom keyboard extensions allow your app to provide an entirely customized keyboard for the user to use. A famous example is the gesture-driven keyboard Swype.

• Document providers allow other applications to access files stored in your app’s sandbox. For example, the Git version control app Working Copy allows other applications to access ...