if([UIDevice currentDevice].userInterfaceIdiom==UIUserInterfaceIdiomPad) {
    //Device is ipad 
}else{
    //Device is iphone
}

为了简单的比较，我总是喜欢宏观:

#define IS_IPOD [[UIDevice currentDevice].model containsString:@"iPod"]
#define IS_IPAD (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad)
#define IS_IPHONE (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPhone)

它简单易用。

你可以像这样使用UIDevice类:

NSString *deviceType = [UIDevice currentDevice].model;

if([deviceType isEqualToString:@"iPhone"])
    // it's an iPhone

请随意使用这个类(gist @ github)

代码已删除并重新定位到 https://gist.github.com/1323251

更新(01/14/11)

显然，这段代码现在有点过时了，但它肯定可以使用Brian Robbins提供的这个线程上的代码进行更新，其中包括更新模型的类似代码。谢谢你在这个帖子上的支持。

我在我的应用程序中使用这个。截至2012年12月。

- (NSString *) platformString {
    // Gets a string with the device model
    size_t size;  
    sysctlbyname("hw.machine", NULL, &size, NULL, 0);  
    char *machine = malloc(size);  
    sysctlbyname("hw.machine", machine, &size, NULL, 0);  
    NSString *platform = [NSString stringWithCString:machine encoding:NSUTF8StringEncoding];  
    free(machine); 

    if ([platform isEqualToString:@"iPhone1,1"])    return @"iPhone 2G";
    if ([platform isEqualToString:@"iPhone1,2"])    return @"iPhone 3G";
    if ([platform isEqualToString:@"iPhone2,1"])    return @"iPhone 3GS";
    if ([platform isEqualToString:@"iPhone3,1"])    return @"iPhone 4";
    if ([platform isEqualToString:@"iPhone3,2"])    return @"iPhone 4";
    if ([platform isEqualToString:@"iPhone3,3"])    return @"iPhone 4 (CDMA)";    
    if ([platform isEqualToString:@"iPhone4,1"])    return @"iPhone 4S";
    if ([platform isEqualToString:@"iPhone5,1"])    return @"iPhone 5";
    if ([platform isEqualToString:@"iPhone5,2"])    return @"iPhone 5 (GSM+CDMA)";

    if ([platform isEqualToString:@"iPod1,1"])      return @"iPod Touch (1 Gen)";
    if ([platform isEqualToString:@"iPod2,1"])      return @"iPod Touch (2 Gen)";
    if ([platform isEqualToString:@"iPod3,1"])      return @"iPod Touch (3 Gen)";
    if ([platform isEqualToString:@"iPod4,1"])      return @"iPod Touch (4 Gen)";
    if ([platform isEqualToString:@"iPod5,1"])      return @"iPod Touch (5 Gen)";

    if ([platform isEqualToString:@"iPad1,1"])      return @"iPad";
    if ([platform isEqualToString:@"iPad1,2"])      return @"iPad 3G";
    if ([platform isEqualToString:@"iPad2,1"])      return @"iPad 2 (WiFi)";
    if ([platform isEqualToString:@"iPad2,2"])      return @"iPad 2";
    if ([platform isEqualToString:@"iPad2,3"])      return @"iPad 2 (CDMA)";
    if ([platform isEqualToString:@"iPad2,4"])      return @"iPad 2";
    if ([platform isEqualToString:@"iPad2,5"])      return @"iPad Mini (WiFi)";
    if ([platform isEqualToString:@"iPad2,6"])      return @"iPad Mini";
    if ([platform isEqualToString:@"iPad2,7"])      return @"iPad Mini (GSM+CDMA)";
    if ([platform isEqualToString:@"iPad3,1"])      return @"iPad 3 (WiFi)";
    if ([platform isEqualToString:@"iPad3,2"])      return @"iPad 3 (GSM+CDMA)";
    if ([platform isEqualToString:@"iPad3,3"])      return @"iPad 3";
    if ([platform isEqualToString:@"iPad3,4"])      return @"iPad 4 (WiFi)";
    if ([platform isEqualToString:@"iPad3,5"])      return @"iPad 4";
    if ([platform isEqualToString:@"iPad3,6"])      return @"iPad 4 (GSM+CDMA)";

    if ([platform isEqualToString:@"i386"])         return @"Simulator";
    if ([platform isEqualToString:@"x86_64"])       return @"Simulator";

    return platform;
}  

要识别iPhone 4S，只需检查以下内容:

var isIphone4S: Bool {

    let width = UIScreen.main.bounds.size.width
    let height = UIScreen.main.bounds.size.height
    let proportions = width > height ? width / height : height / width

    return proportions == 1.5 && UIDevice.current.model == "iPhone"
}