如何区分活动控制器

Question

我在NSHipster上看到了这段代码，但它是如何被调用的？

- (id)activityViewController:(UIActivityViewController *)activityViewController
     itemForActivityType:(NSString *)activityType

if ([activityType isEqualToString:UIActivityTypePostToFacebook]) 
{
    return @"Like this!";
    } else if ([activityType isEqualToString:UIActivityTypePostToTwitter]) {
        return @"Retweet this!";
    } else {
        return nil;
    }
}

我在这里找到了它：http://nshipster.com/uiactivityviewcontroller/

我也有这个叫：

- (void) shareFunction

NSString *textTitle = @"Hello";
NSString *text2 = _@"world";
UIImage *bestPhoto = [[UIImage alloc] initWithData: _photoData];
NSURL *website = [NSURL URLWithString:@"http://www.google.com/"];

NSArray *objectsToShare = @[textTitle, bestyText, bestPhoto, website];

NSArray *includeActivities = @[UIActivityTypeMessage,
                               UIActivityTypeMail,
                               UIActivityTypePostToFacebook,
                               UIActivityTypePostToTwitter,
                               UIActivityTypePostToFlickr];


UIActivityViewController *activityVC = [[UIActivityViewController alloc] initWithActivityItems:objectsToShare applicationActivities:nil];

NSArray *excludeActivities = @[UIActivityTypeAirDrop,
                               UIActivityTypeCopyToPasteboard,
                               UIActivityTypePrint,
                               UIActivityTypeAssignToContact,
                               UIActivityTypeSaveToCameraRoll,
                               UIActivityTypeAddToReadingList,
                               UIActivityTypePostToFlickr,
                               UIActivityTypePostToVimeo];

activityVC.excludedActivityTypes = excludeActivities;

[self presentViewController:activityVC animated:YES completion:nil];
}