Once those views pass out of the viewing area, SwiftUI releases those views so that they no longer take up system resources. For example, as the user scrolls through a stack, views that are currently off screen will only be created once they approach the point of becoming visible to the user. These views (named LazyVStack and LazyHStack) use exactly the same declaration syntax as the traditional stack views, but are designed to only create child views as they are needed. To address this issue, SwiftUI also provides “lazy” vertical and horizontal stack views. While this may not be an issue for most requirements, this can lead to performance degradation in situations where a stack has thousands of child views. When using the traditional HStack and VStack views, the system will create all the views child views at initialization, regardless of whether those views are currently visible to the user. ScrollView is a view which allows the user to scroll through content that extends beyond the visible area of either the containing view or device the screen. This is particularly common when a stack is embedded in a ScrollView. Although the stack examples shown so far contain relatively few child views, it is possible for a stack to contain large quantities of views. So far in this chapter we have only covered the HStack, VStack and ZStack views.
#Swiftui vstack extra argument in call full#
The full book contains 59 chapters and over 520 pages of in-depth information. You are reading a sample chapter from SwiftUI Essentials – iOS 15 Edition.īuy the full book now in eBook (PDF, ePub, and Kindle) or Print format. SwiftUI includes three stack layout views in the form of VStack (vertical), HStack (horizontal) and ZStack (views are layered on top of each other). Once stack views have been explained, this chapter will cover the concept of flexible frames and explain how they can be used to control the sizing behavior of views in a layout. This chapter will introduce the Stack container views included with SwiftUI and explain how they can be used to create user interface designs with relative ease.
SwiftUI also provides a set of layout views for the purpose of defining both how the user interface is organized and the way in which the layout responds to changes in screen orientation and size. User interface design is largely a matter of selecting the appropriate interface components, deciding how those views will be positioned on the screen, and then implementing navigation between the different screens and views of the app.Īs is to be expected, SwiftUI includes a wide range of user interface components to be used when developing an app such as button, label, slider and toggle views.
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