我想在每次应用程序状态更改时做出react .我在听\.applicationState家出版商的 comments :
UIApplication.shared.publisher(for: \.applicationState)
.subscribe(on: DispatchQueue.main)
.sink(receiveCompletion: { completion in
switch completion {
case .finished:
print("finished")
case .failure:
print("failure")
}
}, receiveValue: { state in
print("state", state.rawValue)
})
.store(in: &cancellables)
然而，这只会触发一次(但不会完成).如果我设置应用程序的后台并重新打开它，它不会发布任何新的值.为什么？
您正在使用的发布器适用于符合KVO的属性.(见Performing Key-Value Observing with Combine)但存档的Key-Value Observing Programming Guide号文件警告我们:
Important:并不是所有的类都符合所有属性的KVO.…通常，Apple提供的框架中的属性只有在文档中这样记录时才符合KVO.
但是notification center可以通知我们这些状态变化，例如didBecomeActiveNotification:
NotificationCenter.default
.publisher(for: UIApplication.didBecomeActiveNotification)
.subscribe(on: DispatchQueue.main)
.sink { completion in
switch completion {
case .finished:
print("finished")
case .failure:
print("failure")
}
} receiveValue: { notification in
print("notification", notification)
}
.store(in: &cancellables)
或者，只是:
NotificationCenter.default
.publisher(for: UIApplication.didBecomeActiveNotification)
.subscribe(on: DispatchQueue.main)
.sink { notification in
print("notification", notification)
}
.store(in: &cancellables)
请参见Routing Notifications to Combine Subscribers.有关在SWIFT中创建您自己的符合KVO的类型的信息，请参阅Using Key-Value Observing in Swift.