Iphone 如何获得用户界面习惯用法

我怎样才能获得用户界面习惯用法，我不清楚它是如何工作的，有人能给我指点一下吗

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

从Apple头文件：

/* 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)

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你是说密码吗？还是想了解这个概念