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Editorial Team
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Asked: 2026-05-26T08:39:49+00:00

I create a new project using xcode4.2, and view the AppDelegate: @property (strong, nonatomic)

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I create a new project using xcode4.2, and view the AppDelegate:


@property (strong, nonatomic) UIWindow *window;

I know the strong is a new qualify in Xcode for ARC.However I didn’t select using ARC while creating the project. As a result it is boring me.
Moreover,what does the below mean:


@synthesize window = _window;

Is _window a instance variable? But it didn’t declare in the header file.I can understand if _window declared in the header but failed in this style.
Is it kind of modern obj-c runtime?

thanks!

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1 Answer

  1. Editorial Team

    strong is effectively the same as retain. I’m not sure if the compiler automatically translates that into retain for non ARC code or not. If not, it should generate a warning I would think.

    @synthesize window = _window;

    says the backing instance variable for the property window is _window. In the modern run time for iOS and 64 bit OS X, the instance variable is created automatically if you don’t explicitly declare it in your header.

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