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onChange method
Adds a modifier for this view that fires an action when a specific value changes.
특정 값이 변경되었을 때 view 에 action 을 트리거한다.
Declaration
func onChange<V>(of value: V, perform action: @escaping (V) -> Void) -> some View where V : Equatable
Swift
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Return Value
A view that fires an action when the specified value changes.
Parameters
value The value to check against when determining whether to run the closure.
감시할 밸류를 넣어준다
action A closure to run when the value changes.
감시하는 밸류가 변경되면 취할 액션을 클로져로 넣어준다.
newValue The new value that failed the comparison check.
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.
onChange is called on the main thread. Avoid performing long-running tasks on the main thread. If you need to perform a long-running task in response to value changing, you should dispatch to a background queue.
The new value is passed into the closure. The previous value may be captured by the closure to compare it to the new value. For example, in the following code example, PlayerView passes both the old and new values to the 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) { [playState] newState in
model.playStateDidChange(from: playState, to: newState)
}
}
}
Swift
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