How to share an array between two classes?

Question

I want an array that gets data from one class to be avaliable to me in another class with the same data.
If we declare an array on the applicationDelegate class.
Then declare an object of applicationDelegate in both classes.
And assign the array into appDelegate.array from one class, will i be able get the array across the classes?

Answer 1

Yes, you could declare a member/property on your applicationDelegate class, although you should try to follow the Single Responsibility Principle and make sure you don't end up stuffing lots of miscellaneous shared stuff in your app delegate (which happens a lot with iPhone code).

Another alternative would be to inject the array into the objects' constructors when you create them.

It's hard to know the best solution in terms of design without knowing what this data is and where it really belongs.

Answer 2

I'm with Mike. Leave the App Delegate out of it.

You're in control of when and how your objects are instantiated. If it's important for more than one class to have access to the same data, hand off the data, or a means of getting at your data, as you create instances of the dependent class.

An example, given classes WVParent and WVChild.

WVParent has a property, someArray, which is the array your other objects need:

@interface WVParent : NSObject {

 NSArray *someArray

}
@property (nonatomic, retain) NSArray *someArray;

@end

Then you have WVChild, which itself has a property called parentObject:

@class WVParent;

@interface WVChild : NSObject {

 WVParent *parentObject;

}
@property (nonatomic, assign) WVParent *parentObject;

@end

Assuming the parent is creating the child instance, you'd allocate it and assign the parent:

WVChild *child = [[WVChild alloc] init];
child.parentObject: self;

Then the child instance can access someArray by:

self.parentObject.someArray

This is just one option. You could also just pass the array itself to the child, assuming the data is static and unlikely to change over the course of the application session.

This way, instead of having a source of data living somewhere in the App Delegate, it lives within a class more appropriately responsible for its creation, maintenance and vending. If you've got a class that pops into existence and can only reach the rest of your app by getting the app delegate, you might want to put a little more thought into your architecture.