iOS 获取APP活跃状态

获取APP活跃状态代码如下：

    UIApplicationState state = [UIApplication sharedApplication].applicationState;
    if (state == UIApplicationStateActive){
        NSLog(@"前台活跃状态");
    }else if(state == UIApplicationStateInactive) {
        NSLog(@"不活跃状态");
    }else if(state == UIApplicationStateBackground) {
        NSLog(@"后台状态");
    }

由系统枚举可知苹果官方给我们定义三种状态：

typedef NS_ENUM(NSInteger, UIApplicationState) {
    UIApplicationStateActive,
    UIApplicationStateInactive,
    UIApplicationStateBackground
} API_AVAILABLE(ios(4.0));

UIApplicationStateActive
当前APP处于前台运行。

UIApplicationStateInactive
下拉（iPhone X左上角下拉）状态栏，查看通知消息
上拉（iPhone X右上角下拉）查看快捷键
双击home键，弹出运行中任务栏
应用内拨打电话

UIApplicationStateBackground
当前APP处于后台运行。