SwiftUI uses the @State property wrapper to allow us to modify values inside a struct, which would normally not be allowed because structs are value types. When we put @State before a property, we effectively move its storage out from our struct and into shared storage managed by SwiftUI. This means SwiftUI can destroy and recreate our struct whenever needed (and this can happen a lot!), without losing the state it was storing.
To re-enforce the local nature of @State properties, Apple recommends you mark them as private, like this:
@State private var isFlagged: Bool = false
Example 1: @State and Toggle
struct ContentView: View {
@State private var show: Bool = false
var body: some View {
VStack {
Toggle(isOn: $show, label: {
Text("Label")
}).padding()
if show {
Text("good")
}
}
}
}
Example 2: @State and .onTapGesture
struct ContentView: View {
@State private var isFlipped = false
var body: some View {
VStack {
if isFlipped {
Circle()
.fill(Color.red)
.frame(width: 44, height: 44)
Text("Taylor Swift – 1989")
.font(.headline)
} else {
Text("Taylor Swift – 1989")
.font(.headline)
Circle()
.fill(Color.blue)
.frame(width: 44, height: 44)
}
}
.onTapGesture {
withAnimation {
self.isFlipped.toggle()
}
}
}
}