How to share a variable between multiple Views/XIBs

Question

I've read several similar threads, but can't seem to figure this out - sorry. I've got a project with multiple Views, including a ViewController, several "sub" views, and a NavigationController. I'd like to have an array that is accessible from any of the Views, so that I can populate a TableView or a TextField, etc. I'd like the array to be modifiable from any View that can access it.

Right now I have this in the xxAppDelegate.h file:

NSMutableArray *listOfHeadings;
@property (strong,nonatomic) NSMutableArray *listOfHeadings;

And in the xxAppDelegate.m file I populate the array:

listOfHeadings = [[NSMutableArray alloc] init];
[listOfHeadings addObject:@"Heading 0"];
[listOfHeadings addObject:@"Heading 1"];

But I can't seem to access the array from other .m files. How do I do this correctly?

Answer 1

Since you put your array in xxAppDelegate , you can access your array from any other class like this:

#import "xxAppDelegate.h"
//...
NSMutableArray *array
= [(xxAppDelegate *)[[UIApplication sharedApplication] delegate] listOfHeadings];

Answer 2

While it is true that you could access your app delegate/root controller's property for the array, that would violate principles of encapsulation. Rather than define a single property that all your subview/controller classes will access, pass the array to each class that needs it (you'll still only have one array in memory, and each class will access the same array) at an appropriate time (eg, instantiation).

Another option would be to create an application wide singleton class to provide the array to interested callers.

Answer 3

With the current design you have, you can get ahold of the AppDelegate pointer using:

AppDelegate *dPtr = (AppDelegate *)[[UIApplication sharedApplication] delegate];

Then you can access your array using the property:

[dPtr.your_array objectAtIndex:i];

But I would highly recommend using a Singleton design pattern to manage your global objects.