memcache页面可以更改slab类吗？(Can a memcache page change slab class?)

 你也可以使用下面的方法来启动和停止主线程中的活动指示符，并且还提供了异步执行你的代码的方法， 
 
- (void)showIndicatorAndStartWork
{
    // start the activity indicator (you are now on the main queue)
    [activityIndicator startAnimating];
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        // do your background code here

        dispatch_sync(dispatch_get_main_queue(), ^{
            // stop the activity indicator (you are now on the main queue again)  
        [activityIndicator stopAnimating];
        });
    });
}

You can also use the below method which starts and stops the activity indicator on main thread in a single method, also provides you to execute your code asynchronously as well-
 
- (void)showIndicatorAndStartWork
{
    // start the activity indicator (you are now on the main queue)
    [activityIndicator startAnimating];
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        // do your background code here

        dispatch_sync(dispatch_get_main_queue(), ^{
            // stop the activity indicator (you are now on the main queue again)  
        [activityIndicator stopAnimating];
        });
    });
}