swift - 如何检测 swift 应用程序何时从后台变为前台？

Question

如果应用程序不在后台运行，我想在我的应用程序中运行一个函数。我该怎么做？

我不能使用 applicationDidBecomeActive 和 applicationDidEnterBackground，因为我需要检测它来自后台时的情况，而不是它被带到后台或打开时的状态。还有，第一次打开应用时，从后台来的时候是不会工作的。

Answer 1

检查当前状态:

使用UIApplication.shared.applicationState。

switch UIApplication.shared.applicationState {
case .active: // The app is running in the foreground and currently receiving events.
case .inactive: // The app is running in the foreground but is not receiving events. This might happen as a result of an interruption or because the app is transitioning to or from the background.
case .background: // The app is running in the background.
}