check-if-ios-app-is-in-background.md

检测iOS APP是否在后台

Check if iOS app is in background

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1

App delegate会回调来显示状态改变，你可以利用这个来进行跟踪

同样，UIApplication的属性applicationState 也可以知道状态。

[[UIApplication sharedApplication] applicationState]

typedef NS_ENUM(NSInteger, UIApplicationState) {
    UIApplicationStateActive,
    UIApplicationStateInactive,
    UIApplicationStateBackground
} NS_ENUM_AVAILABLE_IOS(4_0);