Bear Cahill - Using SwiftUI

Any source code or other supplementary material referenced by the author in this book is available to readers on GitHub via the books product page, located at www.apress.com/978-1-4842-6448-5 . For more detailed information, please visit http://www.apress.com/source-code .

Ive included one or more exercises per chapter. Some are shorter and some are longer. In each case, there is also one or more End of Chapter (EOC) zip file of the code for you to review.

Many chapters build on the same code throughout the chapter. So theres only one EOC file with the full result.

The point of each exercise is practice. I want you to go through the process of employing what youre learning. I highly recommend experimenting with variations of the exercises as your curiosity prompts you.

I also strongly encourage repetition . If you repeat an exercise a handful of times to the point that you can just knock it out with familiarity, youll be better off when youre done with this book.

Much of SwiftUI will feel like Swift. Thats good if you know Swift. Youll feel somewhat comfortable passing closures, chaining calls, handling optionals, and so on.

However, SwiftUI has a very state-driven concept to the UI. The user interface is a display of the state. If a value (the state) changes, the UI should reflect that so it needs to render again.

If the value displayed in a TextField is updated, the interface should display the new value. This is done automatically in SwiftUI with binding. Well use property wrappers (similar to how Optional is a type with a wrapped value) to pass these values into controls like the TextField.

The TextField will be updated if the value changes. But also changes in the TextField will be stored in the same place as the item passed in. No more getting the text property and storing SwiftUI cuts out the middle step and just changes the property!

The concept of these property wrappers is tied to the idea of the source of truth . If we have the username or email address stored in a property, that can be the source of truth. If the property changes, the UI is updated. If the user types in a new value, its stored in that same property.

There are different ways of using this concept on value types (e.g., structs) vs. reference types (e.g., classes). Well explore these in detail in this book.

Well also look at how to use an existing UI in a SwiftUI-based app. You may have some existing code that works great, and you want to reuse it. No sense in throwing it away if its still good.

Or you may just not have time to re-create the whole UI in one effort.

Of course, well look at developing interface designs in SwiftUI. But well also look at how to use SwiftUI in Storyboard projects . You may want to migrate to SwiftUI starting in your current UIKit app.

However you decide or need to start using SwiftUI, I hope this book helps get you there.

If you havent used the Combine framework yet , you will in this book. This is not a book on Combine, but parts of it are tightly integrated in things we need to do in SwiftUI.

There are Combine aspects sprinkled throughout this book. Theres also a chapter specifically intended to go a little deeper into Combine. That framework probably deserves its own book, but well dig a bit deeper at times to understand what were doing and using.