onChange(of:initial:_:)
Adds a modifier for this view that fires an action when a specific value changes.
Declaration
nonisolated func onChange<V>(of value: V, initial: Bool = false, _ action: @escaping () -> Void) -> some View where V : Equatable
Parameters
- value:
The value to check against when determining whether to run the closure.
- initial:
Whether the action should be run when this view initially appears.
- action:
A closure to run when the value changes.
Mentioned in
Return Value
A view that fires an action when the specified value changes.
Discussion
You can use onChange to trigger a side effect as the result of a value changing, such as an Environment key or a Binding.
The system may call the action closure on the main actor, so avoid long-running tasks in the closure. If you need to perform such tasks, detach an asynchronous background task.
When the value changes, the new version of the closure will be called, so any captured values will have their values from the time that the observed value has its new value. In the following code example, PlayerView calls into its model when playState changes model.
struct PlayerView: View {
var episode: Episode
@State private var playState: PlayState = .paused
var body: some View {
VStack {
Text(episode.title)
Text(episode.showTitle)
PlayButton(playState: $playState)
}
.onChange(of: playState) {
model.playStateDidChange(state: playState)
}
}
}