iOS判断程序在前台还是后台

[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;
}