onAppear is an extremely crucial lifecycle method in SwiftUI, used to inject key logic when a view is presented. Since view instances may be created and rebuilt frequently, developers often choose to prepare data and perform initialization operations within these methods. In theory, the timing of these lifecycle method calls should be predictable and consistent. However, in certain specific scenarios, onAppear may be called unexpectedly and unnecessarily. This not only can lead to performance overhead but also may cause uncontrollable changes in the application’s state. This article will uncover this easily overlooked SwiftUI behavior trap and provide temporary countermeasures.