如何在if语句中添加#define Objective

Question

我正在制作一个iPhone应用程序，我想做一个宽屏检测，所以我制作了一堆#define，我想用它做一个if声明。

// Device and Widescreen Detection
#define IS_WIDESCREEN ( fabs( ( double )[ [ UIScreen mainScreen ] bounds ].size.height - ( double )568 ) < DBL_EPSILON )

// iPhone
#define IS_IPHONE ( [ [ [ UIDevice currentDevice ] model ] isEqualToString: @"iPhone" ] )  || ( [ [ [ UIDevice currentDevice ] model ] isEqualToString: @"iPhone Simulator" ] ) )
#define IS_IPHONE_5 ( IS_IPHONE && IS_WIDESCREEN )

// iPod Touch
#define IS_IPOD   ( [ [ [ UIDevice currentDevice ] model ] isEqualToString: @"iPod touch" ] )
#define IS_IPOD_5 ( IS_IPOD && IS_WIDESCREEN )

// iPad
#define IS_IPAD (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad)

我想发表一份声明说

if (IS_IPHONE_5) {
...
} else {
...
}

问题是if语句返回一个错误，而XCode一直告诉我这样做

if (IS_IPHONE_5 {
...
} else {
...
}

或者这个

if IS_IPHONE_5 {
...
} else {
...
}

否则就会产生错误。写这个的正确方法是哪一种？

Answer 1

您在IS_IPHONE宏定义中缺少一个括号。你有：

( [ [ [ UIDevice currentDevice ] model ] isEqualToString: @"iPhone" ] )  || ( [ [ [ UIDevice currentDevice ] model ] isEqualToString: @"iPhone Simulator" ] ) )

但你应该：

( ( [ [ [ UIDevice currentDevice ] model ] isEqualToString: @"iPhone" ] )  || ( [ [ [ UIDevice currentDevice ] model ] isEqualToString: @"iPhone Simulator" ] ) )

要查找这些错误，您可以很容易地使用来自菜单Product -> Generate Output -> 预处理文件的命令。这样，您的预处理宏将被展开，您将能够看到最终的代码，因此哪里是错误。

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