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;
}

借用Samrat Mazumdar的回答，这里有一个估算设备屏幕大小的简单方法。它适用于最新的设备，但在未来的设备上可能会失败(正如所有猜测的方法一样)。如果设备正在镜像，它也会混淆(返回设备的屏幕大小，而不是镜像的屏幕大小)

#define SCREEN_SIZE_IPHONE_CLASSIC 3.5
#define SCREEN_SIZE_IPHONE_TALL 4.0
#define SCREEN_SIZE_IPAD_CLASSIC 9.7

+ (CGFloat)screenPhysicalSize
{
    if(UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPhone)
    {
        CGSize result = [[UIScreen mainScreen] bounds].size;
        if (result.height < 500)
            return SCREEN_SIZE_IPHONE_CLASSIC;  // iPhone 4S / 4th Gen iPod Touch or earlier
        else
            return SCREEN_SIZE_IPHONE_TALL;  // iPhone 5
    }
    else
    {
        return SCREEN_SIZE_IPAD_CLASSIC; // iPad
    }
} 

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。

如果项目是用Xcode 6创建的，那么使用下面提到的代码来检测设备。

printf("\nDetected Resolution : %d x %d\n\n",(int)[[UIScreen mainScreen] nativeBounds].size.width,(int)[[UIScreen mainScreen] nativeBounds].size.height);

if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone){
    if ([[UIScreen mainScreen] respondsToSelector: @selector(scale)])
    {
        if([[UIScreen mainScreen] nativeBounds].size.height == 960 || [[UIScreen mainScreen] nativeBounds].size.height == 480){
            printf("Device Type : iPhone 4,4s ");

        }else if([[UIScreen mainScreen] nativeBounds].size.height == 1136){
            printf("Device Type : iPhone 5,5S/iPod 5 ");

        }else if([[UIScreen mainScreen] nativeBounds].size.height == 1334){
            printf("Device Type : iPhone 6 ");

        }else if([[UIScreen mainScreen] nativeBounds].size.height == 2208){
            printf("Device Type : iPhone 6+ ");

        }
    }
}else{
    printf("Device Type : iPad");
}

如果项目是在Xcode 5中创建并在Xcode 6中打开的，那么使用下面提到的代码来检测设备。(如果没有为iPhone 6,6+分配启动图像，此代码有效)

printf("\nDetected Resolution : %d x %d\n\n",(int)[[UIScreen mainScreen] nativeBounds].size.width,(int)[[UIScreen mainScreen] nativeBounds].size.height);
if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone){
    if ([[UIScreen mainScreen] respondsToSelector: @selector(scale)])
    {
       if([[UIScreen mainScreen] nativeBounds].size.height == 960 || [[UIScreen mainScreen] nativeBounds].size.height == 480){
            printf("Device Type : iPhone 4,4s");
            appType=1;
        }else if([[UIScreen mainScreen] nativeBounds].size.height == 1136 || [[UIScreen mainScreen] nativeBounds].size.height == 1704){
            printf("Device Type : iPhone 5,5S,6,6S/iPod 5 ");
            appType=3;
        }
    }
}else{
    printf("Device Type : iPad");
    appType=2;
}

如果你仍然在使用Xcode 5，那么使用下面的代码来检测设备(iPhone 6和6+将不会被检测到)

printf("\nDetected Resolution : %d x %d\n\n",(int)[[UIScreen mainScreen] bounds].size.width,(int)[[UIScreen mainScreen] bounds].size.height);
if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone){
    if ([[UIScreen mainScreen] respondsToSelector: @selector(scale)])
    {
        CGSize result = [[UIScreen mainScreen] bounds].size;
        CGFloat scale = [UIScreen mainScreen].scale;
        result = CGSizeMake(result.width * scale, result.height * scale);
        if(result.height == 960 || result.height == 480){
            printf("Device Type : iPhone 4,4S ");

        }else if(result.height == 1136){
            printf("Device Type : iPhone 5s/iPod 5");

        }
    }
}else{
    printf("Device Type : iPad");

}

用于检测所有版本的iPhone和iPad设备。

#define IS_IPAD (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad)
#define IS_IPHONE (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPhone)
#define IS_IPHONE_5 (IS_IPHONE && [[UIScreen mainScreen] bounds].size.height == 568.0)
#define IS_IPHONE_6 (IS_IPHONE && [[UIScreen mainScreen] bounds].size.height == 667.0)
#define IS_IPHONE_6_PLUS (IS_IPHONE && [[UIScreen mainScreen] bounds].size.height == 736.0)
#define IS_RETINA ([[UIScreen mainScreen] scale] == 2.0) 

在Swift, iOS 8+项目中，我喜欢在UIScreen上做一个扩展，比如:

extension UIScreen {

    var isPhone4: Bool {
        return self.nativeBounds.size.height == 960;
    }

    var isPhone5: Bool {
        return self.nativeBounds.size.height == 1136;
    }

    var isPhone6: Bool {
        return self.nativeBounds.size.height == 1334;
    }

    var isPhone6Plus: Bool {
        return self.nativeBounds.size.height == 2208;
    }

}

(注意:nativeBounds是以像素为单位)。

然后代码会是这样的:

if UIScreen.mainScreen().isPhone4 {
    // do smth on the smallest screen
}

因此，代码清楚地表明这是对主屏幕的检查，而不是对设备模型的检查。