#if 判断条件

不用#if：

NSString*deviceType =[UIDevice currentDevice].model;

if([deviceType isEqualToString:@"iPhone"]){
    //iPhone
}
elseif([deviceType isEqualToString:@"iPod touch"]){
    //iPod Touch
}
else{
    //iPad
}

使用#if：

#ifdefUI_USER_INTERFACE_IDIOM  

 //注意此处没有括号

//UI_USER_INTERFACE_IDIOM 是枚举类型结构体，内有

typedefenum {

#if __IPHONE_3_2 <= __IPHONE_OS_VERSION_MAX_ALLOWED

    UIUserInterfaceIdiomPhone,           // iPhone and iPod touch style UI   0

    UIUserInterfaceIdiomPad,             // iPad style UI                    1

#endif

} UIUserInterfaceIdiom;

 

//而UI_USER_INTERFACE_IDIOM()是定义的宏

#define UI_USER_INTERFACE_IDIOM() ([[UIDevice currentDevice] respondsToSelector:@selector(userInterfaceIdiom)]?[[UIDevice currentDevice] userInterfaceIdiom]:UIUserInterfaceIdiomPhone)

  #define IS_IPAD() (UI_USER_INTERFACE_IDIOM()==UIUserInterfaceIdiomPad)
#else
  #define IS_IPAD() (false)
#endif

#if UI_USER_INTERFACE_IDIOM()==0  //==UIUserInterfaceIdiomPhone
@implementationUINavigationBar(Custom height)

-(CGSize)sizeThatFits:(CGSize)size {
    CGSize newSize =CGSizeMake(self.frame.size.width,44+BreadCrumbBarHeight-1);
    return newSize;
}    
@end
#endif