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I value the opinions on this site and wanted to know what you all thought. I have an app that contains an array. This array is used in several view controllers. Currently, I create the array each time one of the view controllers opens up. I don't believe this to be the best thing to do. I have used NSUserDefaults before, and singletons, but am open to any ideas you have, plist, etc. I am looking on making things run quick and efficient.

Also, I wanted the user to be able to rearrange the array. Lets say it starts out in alpha order. But the user finds it better to rearrange it some other way. I know how to do that, rearrange, but I wanted to know where to keep the original array so that the user can than reset the order back to the original alpha order.

So I guess this question is twofold. Where to store the original array, and how best to then access the changed array throughout the app. Thanks very much for your help.

EDIT #1

I want to thank everyone for their comments and answers! This is what, I feel, the community is about. Learning new and different techniques is great. I am going to attempt to try all the answers (to see if I can actually program it) and see which one works the best for me. Once again thanks for this excellent dialogue.

Edit#2

I ended up doing a bit of both, and I would have never done that without all of your comments and answers. I made the array in the app delegate and saved it in user defaults. It wasn't a basic array, it was an array of custom objects so I had to use a bit of NSCoding. It also was not just alpha sorted, so I made one array that could be manipulated. Once again, thanks for all the great insight!

Douglas
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  • Sounds like the perfect case for a singleton class. Store an `NSArray` with the original order, and a `NSMutableArray` which you reorder. – duci9y Jul 07 '14 at 15:13
  • How big is the array? What sort of things are you storing in it? How many places are you accessing it from? 2? 20? How complex are the things you're storing in it? – Fogmeister Jul 07 '14 at 15:25
  • +1 for @duci96 suggestion – mxb Jul 07 '14 at 15:26
  • @Fogmeister, the array contains about 100 strings that are attributed strings. I access this array in five different views. Thanks. – Douglas Jul 07 '14 at 15:28
  • @Douglas ok, in that case I'd also go with the Singleton idea. You don't have to store the original array though. Just have a method that can sort back to the original sorting. Should be straight forward if it's an alphabetic sort. – Fogmeister Jul 07 '14 at 15:29

3 Answers3

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You can create a singleton instance of it in your AppDelegate. Make an @property for the array in AppDelegate.h, and then import that header into your other viewControllers.

Init and store the array to the appDelegate's array @property in "didLoadWithOptions." You could create custom getters/setters to allow for manipulation. The actual data could come from an external XML, JSON or plist file, but to test you can just hard-code an array in AppDelegate to start with.

Each viewController needs to have a reference to the appDelegate, using the methods described in this answer. You can then access the 1 array as you would any other property, NSArray *dataInVC = myAppDelegate.singletonArray; (...or using NSMutableArray if you want to add/change/manipulate).

...Alternatively, just have a separate class for your data, and create a singleton version of it so you can more easily refactor later if necessary. Examples of how to do this in this answer

Community
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mc01
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I'd recommend storing the array in your app delegate. One of the advantages of this solution is that your app delegate is already a singleton.

Create an NSMutableArray property in your app delegate header file. Init and fill the array in the app delegate didFinishLaunchingWithOptions: method.

Access it from anywhere with the following code :

MyAppDelegate *appDelegate = (MyAppDelegate *)[[UIApplication sharedApplication] delegate];
// appDelegate.myArray holds your values

Going even further, add this to your Prefix.pch file:

#import "MyAppDelegate.h"
#define appDelegate ((MyAppDelegate *)[UIApplication sharedApplication].delegate)

Then the previous code can be reduced simply to calling appDelegate.myArray from anywhere.

You can create methods that handle sorting and other manipulation on your array in your app delegate implementation. If you declare those methods in the app delegate header file, you can also call them from anywhere in the app with :

[appDelegate doStuff:parameter];
rdurand
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  • this tend to bloat the app delegate, it is also valuable to try to keep it slim – mxb Jul 07 '14 at 15:39
  • Why is it "valuable to keep it slim", more than any other singleton object ? (honest question here) – rdurand Jul 07 '14 at 15:40
  • Because after a few singletons your app delegate becomes a huge mess that is impossible to refactor (or test). The app delegates duty is to do application lifecycle related things, not hold custom data. – Kaan Dedeoglu Jul 07 '14 at 15:43
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    As I read here and here, people tend to bloat the app delegate with many things. Big classes are bad for many reasons, regardless the platform. Cocoa Touch is not different. If you have a simple app with only this property in the delegate, this approach could also be fine, but I'd prefer a dedicated singleton for app backing data. – mxb Jul 07 '14 at 15:43
  • I agree, it's a good practice. The best solution is then to create a class, implement the singleton pattern on it, and make it hold and handle the array. – rdurand Jul 07 '14 at 15:49
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As you are accessing your data from five different places, it will soon become confusing to send data to and fro. A singleton class with public properties storing your arrays would be a good solution to this problem.

In case you want to persist the data to disk, NSUserDefaults would be the better option.

Here's how one would go about using NSUserDefaults to do that. For saving data:

[[NSUserDefaults standardUserDefaults] setObject:originalArray forKey:@"OriginalArray"];
[[NSUserDefaults standardUserDefaults] setObject:modifiedArray forKey:@"ModifiedArray"];

Retrieving data:

NSMutableArray *modifiableArray = [[NSUserDefaults standardUserDefaults] arrayForKey:@"ModifiedArray"].mutableCopy;

Don't forget to save the data to disk with a call to [NSUserDefaults synchronize] at appropriate times.

duci9y
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  • I have used NSUserDefaults before and once read that when you publish you don't need the [NSUserDefaults synchronize]. However, I am always to apprehensive about taking it out and have always left it in. What are your thoughts on that? – Douglas Jul 07 '14 at 19:19
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    What `synchronize` does is it saves the changes to disk. Trivia: It is called at regular intervals by the system, but you can never be too sure. – duci9y Jul 07 '14 at 19:20