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Editorial Team
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Asked: 2026-05-29T10:15:04+00:00

This is a two part question in hopes that I can understand more about

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This is a two part question in hopes that I can understand more about the topic.

1) It seems to me that you have two popular options for declaring a property for a class in objective c. One is to add the property to the header’s class body eg.

@interface MyClass : NSObject {
    NSArray *myArray;
}

Or you can add it after the @interface body and before the @end statement like so.

@interface MyClass : NSObject {
    //
}

@property (nonatomic, retain) NSArray *myArray;

What is the difference between these two “styles” and when do you choose one over the other?

2) after the @property you find options such as (nonatomic, retain). What are those for and why/when do you use different options?

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1 Answer

  1. Editorial Team

    Here are the only property modifiers that Xcode recognizes:

    • nonatomic (does not enforce thread safety on the property, mainly for use when only one thread shall be used throughout a program)
    • atomic (enforces thread safety on the property, mainly for use when multiple threads shall be used throughout a program) (default)
    • retain / strong (automatically retains / releases values on set, makes sure values do not deallocate unexpectedly) (default if ARC and object type)
    • readonly (cannot set property)
    • readwrite (can both set and get property) (default)
    • assign / unsafe_unretained (no memory management shall be done with this property, it is handled manually by the person assigning the value) (default if not ARC or object type)
    • copy (copies the object before setting it, in cases where the value set must not change due to external factors (strings, arrays, etc).
    • weak (automatically zeroes the reference should the object be deallocated, and does not retain the value passed in)
    • getter=method (sets the selector used for getting the value of this property)
    • setter= method (set the selector used for setting the value of this property)
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