How can I get UI_USER_INTERFACE_IDIOM

How can I get UI_USER_INTERFACE_IDI开发者_如何学JAVAOM, I am not clear that how does it work, can anyone please guide me?

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if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad)
{
    // iPad device
} else {
    // iPhone / iPod touch device
}

From the Apple Header files:

/* The UI_USER_INTERFACE_IDIOM() macro is provided for use when deploying to a version of the iOS less than 3.2. If the earliest version of iPhone/iOS that you will be deploying for is 3.2 or greater, you may use -[UIDevice userInterfaceIdiom] directly. */
#define UI_USER_INTERFACE_IDIOM() ([[UIDevice currentDevice] respondsToSelector:@selector(userInterfaceIdiom)] ? [[UIDevice currentDevice] userInterfaceIdiom] : UIUserInterfaceIdiomPhone)