CODEWITHSUNDEEP
objective-cproperties
fs_tigre
fs_tigre

Reputation: 10738

Why use @property for NSArrays in iOS

why would you use @property with NSArray?

The reason for my question is because I was under the impression that @properties were mainly used to take advantage of the getter and setter you get for free when you use @property, but when you assign an NSArray to a property you know you will never use the getter and setter to access the objects in the array, why use properties on this case. Does this have to do with ARC, in other words is this considered a better memory management practice?

Upvotes: 0

Views: 115

Answers (4)

Caleb
Caleb

Reputation: 124997

but when you assign an NSArray to a property you know you will never use the getter and setter to access the objects in the array, why use properties on this case.

For the same reasons that you use properties for other objects:

  • accessors: The accessors are for the array itself, not objects in the array. It's not uncommon to get or set an entire array at once:

    NSArray *kids = frank.children;                 // get the array
mary.children = @[@"Nick", @"Sam", @"Susan"];   // set the array

  • abstraction: Using properties instead of accessing the underlying array directly makes it easier to change the implementation later, should that become necessary.

  • KVC compliance: You get it for free with properties. With collections like arrays, KVC gives you a lot of power. You can use collection operators like @avg and @max as well as indexed accessors:

    int employees = [accounting countOfEmployees];  // same as [accounting.employees count]
Employee *thirdEmployee = [engineering objectInEmployeesAtIndex:2];  // same as [engineering.employees objectAtIndex:2]

Upvotes: 2

Gabriele Petronella
Gabriele Petronella

Reputation: 108101

Along with what already said by other answers, I usually like to copy my array for security purposes.

If you're accepting an NSArray by the client, she could potentially provide you a NSMutableArray instance. If that's the case and you want to ensure that the array you're working with doesn't change unexpectedly, you'd better copy it as opposed to retain it.

Properties come in handy in this case since you can declare

@property (nonatomic, copy) NSArray * myArray;

and be sure that you're the only owner of that array after you assigned it.

I typically use this strategy for any class with mutable subclasses, such as NSString, NSArray, NSSet and so on, whenever I care about the ownership of the data.

The downside of this strategy is of course memory efficiency, but in the end engineering is the art of intelligent compromise.

Upvotes: 3

rmaddy
rmaddy

Reputation: 318804

You use a property to get or set the whole array. You also use the property to access individual elements of the array.

Using a property with an array has nothing to do with ARC or MRC. Properties are a way to encapsulate data. That's it.

If you don't wish to provide access to the whole array then don't use a property. Add method(s) to set/get individual elements of the internal array if that is appropriate.

Upvotes: 4

Mark McCorkle
Mark McCorkle

Reputation: 9414

To use the array outside of a single method or class. ClassA.array = ClassB.array; or to simply read from the array in a different method of the same class since the array will dealloc immediately after execution.

Upvotes: 2

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