依赖规模在很多层面上都是错误的。如果我们问系统呢?

- (NSString *) getDeviceModel
{
    struct utsname systemInfo;
    uname(&systemInfo);
    return [NSString stringWithCString:systemInfo.machine encoding:NSUTF8StringEncoding];
}

摘自《检测硬件类型的最佳方法，iPhone4还是iPhone5?》edzio27回答。

CGFloat height = [UIScreen mainScreen].bounds.size.height;

NSLog(@"screen soze is %f",height);

  if (height>550) {

          // 4" screen-do some thing
     }

  else if (height<500) {

        // 3.5 " screen- do some thing

     }

这是我们的代码，在ios7/ios8上测试通过，适用于iphone4、iphone5、ipad、iphone6、iphone6p，无论在设备上还是模拟器上:

#define IS_IPAD (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad)
#define IS_IPHONE (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPhone) // iPhone and       iPod touch style UI

#define IS_IPHONE_5_IOS7 (IS_IPHONE && [[UIScreen mainScreen] bounds].size.height == 568.0f)
#define IS_IPHONE_6_IOS7 (IS_IPHONE && [[UIScreen mainScreen] bounds].size.height == 667.0f)
#define IS_IPHONE_6P_IOS7 (IS_IPHONE && [[UIScreen mainScreen] bounds].size.height == 736.0f)
#define IS_IPHONE_4_AND_OLDER_IOS7 (IS_IPHONE && [[UIScreen mainScreen] bounds].size.height < 568.0f)

#define IS_IPHONE_5_IOS8 (IS_IPHONE && ([[UIScreen mainScreen] nativeBounds].size.height/[[UIScreen mainScreen] nativeScale]) == 568.0f)
#define IS_IPHONE_6_IOS8 (IS_IPHONE && ([[UIScreen mainScreen] nativeBounds].size.height/[[UIScreen mainScreen] nativeScale]) == 667.0f)
#define IS_IPHONE_6P_IOS8 (IS_IPHONE && ([[UIScreen mainScreen] nativeBounds].size.height/[[UIScreen mainScreen] nativeScale]) == 736.0f)
#define IS_IPHONE_4_AND_OLDER_IOS8 (IS_IPHONE && ([[UIScreen mainScreen] nativeBounds].size.height/[[UIScreen mainScreen] nativeScale]) < 568.0f)

#define IS_IPHONE_5 ( ( [ [ UIScreen mainScreen ] respondsToSelector: @selector( nativeBounds ) ] ) ? IS_IPHONE_5_IOS8 : IS_IPHONE_5_IOS7 )
#define IS_IPHONE_6 ( ( [ [ UIScreen mainScreen ] respondsToSelector: @selector( nativeBounds ) ] ) ? IS_IPHONE_6_IOS8 : IS_IPHONE_6_IOS7 )
#define IS_IPHONE_6P ( ( [ [ UIScreen mainScreen ] respondsToSelector: @selector( nativeBounds ) ] ) ? IS_IPHONE_6P_IOS8 : IS_IPHONE_6P_IOS7 )
#define IS_IPHONE_4_AND_OLDER ( ( [ [ UIScreen mainScreen ] respondsToSelector: @selector( nativeBounds ) ] ) ? IS_IPHONE_4_AND_OLDER_IOS8 : IS_IPHONE_4_AND_OLDER_IOS7 )

这里是正确的测试设备，不依赖于方向

- (BOOL)isIPhone5
{
    CGSize size = [[UIScreen mainScreen] bounds].size;
    if (MIN(size.width,size.height) == 320 && MAX(size.width,size.height == 568)) {
        return YES;
    }
    return NO;
}

这是我的cocos2d项目的宏。对于其他应用程序应该是一样的。

#define WIDTH_IPAD 1024
#define WIDTH_IPHONE_5 568
#define WIDTH_IPHONE_4 480
#define HEIGHT_IPAD 768
#define HEIGHT_IPHONE 320

#define IS_IPHONE (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPhone)
#define IS_IPAD (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad)

//width is height!
#define IS_IPHONE_5 ( [ [ UIScreen mainScreen ] bounds ].size.height == WIDTH_IPHONE_5 )
#define IS_IPHONE_4 ( [ [ UIScreen mainScreen ] bounds ].size.height == WIDTH_IPHONE_4 )

#define cp_ph4(__X__, __Y__) ccp(cx_ph4(__X__), cy_ph4(__Y__))
#define cx_ph4(__X__) (IS_IPAD ? (__X__ * WIDTH_IPAD / WIDTH_IPHONE_4) : (IS_IPHONE_5 ? (__X__ * WIDTH_IPHONE_5 / WIDTH_IPHONE_4) : (__X__)))
#define cy_ph4(__Y__) (IS_IPAD ? (__Y__ * HEIGHT_IPAD / HEIGHT_IPHONE) : (__Y__))

#define cp_pad(__X__, __Y__) ccp(cx_pad(__X__), cy_pad(__Y__))
#define cx_pad(__X__) (IS_IPAD ? (__X__) : (IS_IPHONE_5 ? (__X__ * WIDTH_IPHONE_5 / WIDTH_IPAD) : (__X__ * WIDTH_IPHONE_4 / WIDTH_IPAD)))
#define cy_pad(__Y__) (IS_IPAD ? (__Y__) : (__Y__ * HEIGHT_IPHONE / HEIGHT_IPAD))

在Swift 3中，你可以使用我的简单类KRDeviceType。

https://github.com/ulian-onua/KRDeviceType

它有很好的文档，并支持运算符==，>=，<=。

例如，要检测设备是否有iPhone 6/6s/7的边界，你可以使用next比较:

if KRDeviceType() == .iPhone6 {
// Perform appropiate operations
}

要检测设备是否有iPhone 5/5S/SE或更早(iPhone 4s)的边界，您可以使用下一个比较:

if KRDeviceType() <= .iPhone5 {   //iPhone 5/5s/SE of iPhone 4s
// Perform appropiate operations (for example, set up constraints for those old devices)
}