It’s been a while since I started learning SwiftUI but the framework has only matured in the last month or so. A lot of things changed since the first developer’s beta in June — gone are NavigationButton, PresentationButton and a ton of UI elements has seen a change in implementation.
But as we near Apple’s September Xcode GM launch, now is a good time as any to learn about SwiftUI and see the framework with fresh eyes and entirely new mindset. With SwiftUI, everything is a View — a Button, a Toggle, a TextField — everything. View is a function of @State; variables declared as a @State are managed by SwiftUI, and a change in value will cause subscribing Views to update and render.
I’m still trying to wrap my head around how things work in the old UIKit framework, but I’ll start with passing data around SwiftUI Views.
-
Use
@Stateto declare a source of truth; it is available within the currentView. -
Use
@Bindingto link to@Statevariables in anotherView. Doing this makes sure you have one source of truth, and you don’t need to worry about keeping them in sync.
struct ParentView: View {
@State var isGreen: Bool = true
var body: some View {
Rectangle().fill(isGreen ? Color.green : Color.primary)
ChildView(isGreen: $isGreen)
}
}
struct ChildView: View {
@Binding var isGreen: Bool
var body: some View {
Toggle(isOn: $isGreen) {
Text("Background")
}
}
}
-
Use
@ObservableObjectto define your own data model that is passed aroundViews. -
Use
@Environment@EnvironmentObjectto allowViews to read data directly from the environment, instead of having to have the object passed aroundViews.
Some videos and articles I found particularly helpful are:
- Data flow in SwiftUI - Apple’s WWDC video
- Making apps with Core Data - Apple’s WWDC video – There’s a specific section on how the new features in Core Data will enable List View in SwiftUI
- Majid’s example of how Property Wrappers work