[UIApplication sharedApplication].applicationState will return current state, check it possible values and don’t create unnecessary flags when you can use system features.
Values you may want to consider:
UIApplicationStateActive（前台）
UIApplicationStateInactive（收到通知）
UIApplicationStateBackground（后台）
e.g.
+(BOOL) runningInBackground
{
UIApplicationState state = [UIApplication sharedApplication].applicationState;
BOOL result = (state == UIApplicationStateBackground);
return result;
}
+(BOOL) runningInForeground
{
UIApplicationState state = [UIApplication sharedApplication].applicationState;
BOOL result = (state == UIApplicationStateActive);
return result;
}
