#class cluster

Why?

A few things come to mind:

Makes it simpler to support an older iOS, different hardware, etc

Cleans code of frequent if-then checks

Allows easy integration of newer iOS version-aware classes without modifying much/any of your existing code

A Use Case

When deciding if I wanted to support both iOS 6 and iOS 7 with both an app I have in the App Store and an app I'm working on, I did some digging around, and found a post by Jean-David Gadina (http://www.noxeos.com/2013/06/18/strategies-support-ios7-ui/) incredibly helpful for making your code support both versions of the OS without needing to write a bunch of if-then's in your code. I was also at the time monkeying around with the new UISearchDisplayController goodness of having them embedded in navigation bars in iOS 7 and wondering why it would work on the iPhone but not the iPad. After quite a bit of banging my head on the desk, and reading and re-reading Apple's docs on UISDC, I looked around the internets, and found an article by Peter Steinberger (http://petersteinberger.com/blog/2013/fixing-uisearchdisplaycontroller-on-ios-7/) where he described what he did to fix the UISDC on iOS 7 iPad version. And then I had my "a ha" moment -- I could use Class Clusters to figure out which iOS was running, and display a UISDC accordingly. So let's do it.

The Code.

The code is available on my GitHub page (https://github.com/SixFiveSoftware/ClusterDemo), if you'd like to look at it; I will quickly run through the steps of creating it here. Since I suggest downloading the code, I won't cover absolutely everything to make a working app here, just the pertinent parts.

Firstly, create a category on UIDevice to return the system major version (i.e., '6' or '7', or '8' in the future, etc.). Create a new file, a Category on UIDevice, called UIDevice+VersionCheck. You'll want to declare the method in your .h interface:

- (NSUInteger)systemMajorVersion;

Then, in your .m implementation file, type this method:

- (NSUInteger)systemMajorVersion {     NSString *versionString = [self systemVersion];     return (NSUInteger)[versionString doubleValue]; }

Next, let's create the cluster. Because I wanted this to display search results, create a new subclass of UITableViewController, and call it whatever you want to make it (hint: keep it general, like Apple did with NSArray, NSNumber, etc.).  Here, I made mine SFSSearchTVC. Then, create two more classes, each one a subclass of SFSSearchTVC (or whatever you called yours). I called my SFSSearchTVC6 and SFSSearchTVC7, for (you guessed it) iOS 6 and iOS 7. The reason we want to subclass is so that we can reuse methods because of inheritance.

Since iOS 6 search display controllers didn't suck, we won't have to do much to the iOS 6 subclass. The iOS 7 one, however, takes some work. Let's first do that voodoo to make the cluster work.

Open SFSSearchTVC and override -alloc:

+ (id)alloc {     if ([self class] == [SFSSearchTVC class]) {         if ([UIDevice currentDevice] systemMajorVersion] < 7) {             return [SFSSearchTVC6 alloc];         } else if ([UIDevice currentDevice] systemMajorVersion] == 7) {             return [SFSSearchTVC7 alloc];         }     }     return [super alloc]; }

This method gets called first thing when the you need an SFSSearchTVC object, so you override this method to direct it to which class to return. A lot easier than you thought, isn't it?  Basically it's checking your systemMajorVersion and returning the appropriate subclass; if none of these are true, it just simply returns[super alloc].

Now, just customize the iOS 6 and iOS 7 subclasses how you want them, and when you alloc/init an SFSSearchTVC object, you'll get one according to your iOS version! 

Wrap Up

At this point, download the code from https://github.com/SixFiveSoftware/ClusterDemo and play around with it yourself. You'll see that the SFSSearchTVC is the UISearchBar delegate, but not the UISearchDisplayController delegate; it leaves that to each subclass for how to handle that.

Hope this helps!