With all great programming languages come great frameworks—in particular, UI frameworks. In the case of Apple, UIKit has been the UI framework of choice since Objective-C, offering everything from labels, fonts, and buttons, to animation.

Written in Objective-C, UIKit has been the binding of the iPhone UI for all developers since the beginning. With a multitude of public APIs and documentation available to developers and solid support from the community, there has been little else to offer in terms of alternatives for Apple development.

Without UIKit, everyday interactions such as tap, pinch, and zoom gestures for drawing wouldn’t be available. UIKit is even responsible for accessibility, which we'll touch on later on in this book.

The binding between UIKit and Swift can be performed in two ways: programmatically or through the Interface Builder.

Creating the UI programmatically involves writing around five lines of code, such as in the following example:

As seen in the preceding screenshot, you first need to create an instance of the UIButton, set the frame (origin and size), set the background color, give the button's label some text, set a tap gesture (what happens when you tap the button), and then add the gesture to the button.

All this is done before we even place the button within our view hierarchy, not to mention writing the code to determine what happens when we tap the button.

All in all, quite a few lines of code—for something that could end up being a simple operation.

The second way is via Xcode's Interface Builder. Interface Builder is a built-in graphical user interface (GUI) that allows you to use either XML Interface Builder (XIB) files, NeXTSTEP Interface Builder (NIB) files, or Storyboards to design and create your layout with ease. With Interface Builder, you can simply drag and drop components such as Views (UIView), labels (UILabel), and Image Views (UIImageView) straight onto a canvas that can be wired straight into your code. The following is an example of how a button is created in Interface Builder and shows the code to handle the button's tap event:

Although highly regarded by the Apple community, with the introduction of Swift UIKit slowly started to show its age. Swift's clean and compact syntax started to look bloated and untidy when asked to perform simple tasks, such as creating a frame for a button or performing an animation.

Many thought that this was simply how it was going to be from now on, with a focus on bringing UIKit to macOS deemed to be a greater necessity. But little did we know that Apple was about to change the way we build apps, for the foreseeable future.

In June 2019, at WWDC, Apple introduced us to SwiftUI.