下面的代码有助于获得UDID:

        udid = [[[UIDevice currentDevice] identifierForVendor] UUIDString];
        NSLog(@"UDID : %@", udid);

获得UDID的有效方法:

Launch a web server inside the app with two pages: one should return specially crafted MobileConfiguration profile and another should collect UDID. More info here, here and here. You open the first page in Mobile Safari from inside the app and it redirects you to Settings.app asking to install configuration profile. After you install the profile, UDID is sent to the second web page and you can access it from inside the app. (Settings.app has all necessary entitlements and different sandbox rules).

一个使用RoutingHTTPServer的例子:

import UIKit
import RoutingHTTPServer

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    var bgTask = UIBackgroundTaskInvalid
    let server = HTTPServer()

    func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
        application.openURL(NSURL(string: "http://localhost:55555")!)
        return true
    }

    func applicationDidEnterBackground(application: UIApplication) {
        bgTask = application.beginBackgroundTaskWithExpirationHandler() {
            dispatch_async(dispatch_get_main_queue()) {[unowned self] in
                application.endBackgroundTask(self.bgTask)
                self.bgTask = UIBackgroundTaskInvalid
            }
        }
    }
}

class HTTPServer: RoutingHTTPServer {
    override init() {
        super.init()
        setPort(55555)
        handleMethod("GET", withPath: "/") {
            $1.setHeader("Content-Type", value: "application/x-apple-aspen-config")
            $1.respondWithData(NSData(contentsOfFile: NSBundle.mainBundle().pathForResource("udid", ofType: "mobileconfig")!)!)
        }
        handleMethod("POST", withPath: "/") {
            let raw = NSString(data:$0.body(), encoding:NSISOLatin1StringEncoding) as! String
            let plistString = raw.substringWithRange(Range(start: raw.rangeOfString("<?xml")!.startIndex,end: raw.rangeOfString("</plist>")!.endIndex))
            let plist = NSPropertyListSerialization.propertyListWithData(plistString.dataUsingEncoding(NSISOLatin1StringEncoding)!, options: .allZeros, format: nil, error: nil) as! [String:String]

            let udid = plist["UDID"]! 
            println(udid) // Here is your UDID!

            $1.statusCode = 200
            $1.respondWithString("see https://developer.apple.com/library/ios/documentation/NetworkingInternet/Conceptual/iPhoneOTAConfiguration/ConfigurationProfileExamples/ConfigurationProfileExamples.html")
        }
        start(nil)
    }
}

下面是udid.mobileconfig的内容:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
    <dict>
        <key>PayloadContent</key>
        <dict>
            <key>URL</key>
            <string>http://localhost:55555</string>
            <key>DeviceAttributes</key>
            <array>
                <string>IMEI</string>
                <string>UDID</string>
                <string>PRODUCT</string>
                <string>VERSION</string>
                <string>SERIAL</string>
            </array>
        </dict>
        <key>PayloadOrganization</key>
        <string>udid</string>
        <key>PayloadDisplayName</key>
        <string>Get Your UDID</string>
        <key>PayloadVersion</key>
        <integer>1</integer>
        <key>PayloadUUID</key>
        <string>9CF421B3-9853-9999-BC8A-982CBD3C907C</string>
        <key>PayloadIdentifier</key>
        <string>udid</string>
        <key>PayloadDescription</key>
        <string>Install this temporary profile to find and display your current device's UDID. It is automatically removed from device right after you get your UDID.</string>
        <key>PayloadType</key>
        <string>Profile Service</string>
    </dict>
</plist>

配置文件安装将失败(我没有费心实现预期的响应，请参阅文档)，但应用程序将获得正确的UDID。你还应该在mobileconfig上签名。

从ios6开始，我们有了NSUUID类，它符合RFC4122

Apple Link: apple_ref for NSUUID

根据@moonlight提出的链接，我做了几次测试，这似乎是最好的解决方案。正如@DarkDust所说，该方法将检查始终可用的en0。 有两种选择: uniqueDeviceIdentifier (MAC+CFBundleIdentifier的MD5) 和uniqueGlobalDeviceIdentifier(MAC的MD5)，这些总是返回相同的值。 下面是我所做的测试(用真正的设备):

#import "UIDevice+IdentifierAddition.h"

NSLog(@"%@",[[UIDevice currentDevice] uniqueDeviceIdentifier]);
NSLog(@"%@",[[UIDevice currentDevice] uniqueGlobalDeviceIdentifier]);

XXXX21f1f19edff198e2a2356bf4XXXX - (WIFI)UDID XXXX7dc3c577446a2bcbd77935bdXXXX - (WIFI)GlobalAppUDID XXXX21f1f19edff198e2a2356bf4XXXX - (3G)UDID XXXX7dc3c577446a2bcbd77935bdXXXX - (3G)GlobalAppUDID XXXX21f1f19edff198e2a2356bf4XXXX - (GPRS)UDID XXXX7dc3c577446a2bcbd77935bdXXXX - (GPRS)GlobalAppUDID XXXX21f1f19edff198e2a2356bf4XXXX - (AirPlane mode)UDID XXXX7dc3c577446a2bcbd77935bdXXXX - (AirPlane mode)GlobalAppUDID XXXX21f1f19edff198e2a2356bf4XXXX - (Wi-Fi)after removing and reinstalling the app XXXX7dc3c577446a2bcbd77935bdXXXX (Wi-Fi) after removing and installing the app

希望对大家有用。

编辑: 正如其他人指出的那样，这个解决方案在iOS 7中不再有用，因为uniqueIdentifier不再可用，查询MAC地址现在总是返回02:00:00:00:00:00

如果有人在寻找替代方案时偶然发现了这个问题。我在IDManager课上就采用了这种方法， 这是不同解的集合。KeyChainUtil是一个从keychain读取的包装器。 您还可以使用散列MAC地址作为一种唯一ID。

/*  Apple confirmed this bug in their system in response to a Technical Support Incident 
    request. They said that identifierForVendor and advertisingIdentifier sometimes 
    returning all zeros can be seen both in development builds and apps downloaded over the 
    air from the App Store. They have no work around and can't say when the problem will be fixed. */
#define kBuggyASIID             @"00000000-0000-0000-0000-000000000000"

+ (NSString *) getUniqueID {
    if (NSClassFromString(@"ASIdentifierManager")) {
        NSString * asiID = [[[ASIdentifierManager sharedManager] advertisingIdentifier] UUIDString];
        if ([asiID compare:kBuggyASIID] == NSOrderedSame) {
            NSLog(@"Error: This device return buggy advertisingIdentifier.");
            return [IDManager getUniqueUUID];
        } else {
            return asiID;
        }

    } else {
        return [IDManager getUniqueUUID];
    }
}


+ (NSString *) getUniqueUUID {
    NSError * error;
    NSString * uuid = [KeychainUtils getPasswordForUsername:kBuyassUser andServiceName:kIdOgBetilngService error:&error];
    if (error) {
        NSLog(@"Error geting unique UUID for this device! %@", [error localizedDescription]);
        return nil;
    }
    if (!uuid) {
        DLog(@"No UUID found. Creating a new one.");
        uuid = [IDManager GetUUID];
        uuid = [Util md5String:uuid];
        [KeychainUtils storeUsername:USER_NAME andPassword:uuid forServiceName:SERVICE_NAME updateExisting:YES error:&error];
        if (error) {
            NSLog(@"Error getting unique UUID for this device! %@", [error localizedDescription]);
            return nil;
        }
    }
    return uuid;
}

/* NSUUID is after iOS 6. */
+ (NSString *)GetUUID
{
    CFUUIDRef theUUID = CFUUIDCreate(NULL);
    CFStringRef string = CFUUIDCreateString(NULL, theUUID);
    CFRelease(theUUID);
    return [(NSString *)string autorelease];
}

#pragma mark - MAC address
// Return the local MAC addy
// Courtesy of FreeBSD hackers email list
// Last fallback for unique identifier
+ (NSString *) getMACAddress
{
    int                 mib[6];
    size_t              len;
    char                *buf;
    unsigned char       *ptr;
    struct if_msghdr    *ifm;
    struct sockaddr_dl  *sdl;

    mib[0] = CTL_NET;
    mib[1] = AF_ROUTE;
    mib[2] = 0;
    mib[3] = AF_LINK;
    mib[4] = NET_RT_IFLIST;

    if ((mib[5] = if_nametoindex("en0")) == 0) {
        printf("Error: if_nametoindex error\n");
        return NULL;
    }

    if (sysctl(mib, 6, NULL, &len, NULL, 0) < 0) {
        printf("Error: sysctl, take 1\n");
        return NULL;
    }

    if ((buf = malloc(len)) == NULL) {
        printf("Error: Memory allocation error\n");
        return NULL;
    }

    if (sysctl(mib, 6, buf, &len, NULL, 0) < 0) {
        printf("Error: sysctl, take 2\n");
        free(buf); // Thanks, Remy "Psy" Demerest
        return NULL;
    }

    ifm = (struct if_msghdr *)buf;
    sdl = (struct sockaddr_dl *)(ifm + 1);
    ptr = (unsigned char *)LLADDR(sdl);
    NSString *outstring = [NSString stringWithFormat:@"%02X:%02X:%02X:%02X:%02X:%02X", *ptr, *(ptr+1), *(ptr+2), *(ptr+3), *(ptr+4), *(ptr+5)];

    free(buf);
    return outstring;
}

+ (NSString *) getHashedMACAddress
{
    NSString * mac = [IDManager getMACAddress];
    return [Util md5String:mac];
}

+ (NSString *)md5String:(NSString *)plainText
{
    if(plainText == nil || [plainText length] == 0)
        return nil;

    const char *value = [plainText UTF8String];
    unsigned char outputBuffer[CC_MD5_DIGEST_LENGTH];
    CC_MD5(value, strlen(value), outputBuffer);

    NSMutableString *outputString = [[NSMutableString alloc] initWithCapacity:CC_MD5_DIGEST_LENGTH * 2];
    for(NSInteger count = 0; count < CC_MD5_DIGEST_LENGTH; count++){
        [outputString appendFormat:@"%02x",outputBuffer[count]];
    }
    NSString * retString = [NSString stringWithString:outputString];
    [outputString release];
    return retString;
}

也许你可以用:

[UIDevice currentDevice].identifierForVendor.UUIDString

苹果的文档对identifierforvendor的描述如下:

对于运行在同一设备上的来自同一供应商的应用程序，此属性的值是相同的。对于同一设备上来自不同供应商的应用程序，以及不同设备上的应用程序，无论供应商如何，都会返回不同的值。