MAIKit

MAIKit (Mac and iOS Kit) is a framework for sharing code between OS X and iOS.

UIKit contains many classes which have counterparts in Appkit. These classes contain many, but not all of the same methods and properties. For example, UIColor and NSColor are nearly identical, but NSColor contains constructors for creating colors from calibrated and device values, which UIColor does not, and UIColor has a CIColor property, which NSColor does not.

Many projects use @compatibility_alias to alias UIColor to NSColor in order to share code between iOS and OS X apps. However, this approach has some drawbacks. One such drawback is that it is still possible to write and compile code that works on one platform but not the other. For example, the following code would compile for iOS, but not OS X.

let ciColor = NSColor.blackColor().CIColor

Of course, this error would be easily caught the next time the code was compiled for OS X, but constantly compiling for both platforms slows down development. Furthermore, it takes longer to correct problems than to prevent them, and when working on a team, if the build error is not caught before it is committed, could prevent other team members from completing their work until it is fixed. The @compatibility_alias method also exposes platform-specific methods and properties to autocomplete, leaving to the developer the responsibility of remembering which APIs are available on both platforms, and which APIs are not.

MAIKit aims to prevent these problems, speeding up cross-platform development. It does so by defining protocols which contain the intersection of methods and properties of UIKit and AppKit classes. It also defines classes which implement these protocols, and can be used in both iOS and OS X code. These classes inherit from their UIKit and Appkit counterparts, and can be safely subclassed.

Continuing the NSColor example, MAIKit defines a class named MAIColor, and a protocol named MAIColorProtocol. The same pattern applies to all UIKit and AppKit classes.

When declaring variables, you will need to declare them as MAIKit-defined protocols in Swift, or as Objective-C objects conforming to those protocols. You cannot instantiate protocols, however, so you will need to initialize them using MAIKit-defined classes.

let maiColor : MAIColorProtocol = MAIColor.blackColor()
let cgColor = maiColor.CGColor