Book Image

SwiftUI Essentials – iOS 14 Edition

By : Neil Smyth
Book Image

SwiftUI Essentials – iOS 14 Edition

By: Neil Smyth

Overview of this book

Do you want to create iOS apps with SwiftUI, Xcode 12, and Swift 5.3, and want to publish it on the app store? This book helps you achieve these skills with a step-by-step approach. This course first walks you through the steps necessary to set up an iOS development environment together and introduces Swift Playgrounds to learn and experiment with Swift—specifically, the Swift 5.3 programming language. After establishing key concepts of SwiftUI and project architecture, this course provides a guided tour of Xcode in SwiftUI development mode. The book also covers the creation of custom SwiftUI views and explains how these views are combined to create user interface layouts, including the use of stacks, frames, and forms. One of the more important skills you’ll learn is how to integrate SwiftUI views into existing UIKit-based projects and explain the integration of UIKit code into SwiftUI. Finally, the book explains how to package up a completed app and upload it to the app store for publication. Along the way, the topics covered in the book are put into practice through detailed tutorials, the source code for which is also available for download. By the end of this course, you will be able to build your own apps for iOS 14 using SwiftUI and publish it on the app store. The code files for the book can be found here: https://www.ebookfrenzy.com/retail/swiftui-ios14/
Table of Contents (56 chapters)
56
Index

37.4 The updating Callback Action

The updating callback action is like onChanged with the exception that it works with a special property wrapper named @GestureState. GestureState is like the standard @State property wrapper but is designed exclusively for use with gestures. The key difference, however, is that @GestureState properties automatically reset to the original state when the gesture ends. As such, the updating callback is ideal for storing transient state that is only needed while a gesture is being performed.

Each time an updating action is called, it is passed the following three arguments:

DragGesture.Value instance containing information about the gesture.

A reference to the @GestureState property to which the gesture has been bound.

A Transaction object containing the current state of the animation corresponding to the gesture.

The DragGesture.Value instance is particularly useful and contains the following properties:

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