What is the strong property attribute

I am using the Xcode beta for developers, and am noticing some subtle differences. Among them is a new attribute for declared properties.

@property(strong)IBOutlet NSArrayController *arrayControl;

My question is: what does the strong attribute mean?? Does it replace some older one, or is it something entirely new? I have searched through google and the developer documentation and havent been able to find anything. Until i know what it is i am hesitant to use it.

Thanks in advance

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最佳答案

It's a replacement for the retain attribute, as part of Objective-C Automated Reference Counting (ARC). In non-ARC code it's just a synonym for retain.

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As we know, we cannot release any object in an ARC-based project in iOS 5. So when we want to retain any object for further use at a later stage and don't want ARC to remove the object from memory, then we set the property for the object as "Strong".

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A strong reference is a reference to an object that stops it from being deallocated. In other words it creates a owner relationship. Whereas previously you would do this:

**// Non-ARC Compliant Declaration
@property(retain) NSObject *obj;**

Under ARC we do the following to ensure a class instance takes an ownership interest a referenced object (i.e. so it cannot be deallocated until the owner is).

**// ARC Compliant Declaration
@property(strong) NSObject *obj;**