蘋果本著為使用者安全考慮的初衷導致UDID和Mac地址相繼陣亡，IMEI也不例外，為了裝置的唯一性，一代代開發者絞盡腦汁，後來KeyChain被他們瞄上了，終於可以繼續判別社別的唯一性。

原理是利用UUID，有人說，UUID是非唯一的，很容易變化，對，沒錯，但是UUID絕對不會重複對吧？所以UUID我只需要獲取一次，然後存入KeyChain，即使App被刪除了，KeyChain中的UUID也不會被刪除，如果你們公司有兩款App，完全可以通過存入的key值讀取出另一個App的UUID，做一些簡單的互動。

具體的實現方法，網上有很多種方法，很少有全套的使用方法，博主這裡重新總結了下：
先說說獲取UUID的方法：

 CFUUIDRef myUUID = CFUUIDCreate( nil );
    CFStringRef uuidString = CFUUIDCreateString( nil, myUUID );
    NSString * result = (NSString *)CFBridgingRelease(CFStringCreateCopy( NULL, uuidString));

關於實際的儲存，都是屬於套路的程式碼了，沒什麼可讀性，直接貼出來了：
有兩個管理類：

#import <Foundation/Foundation.h>

@interface LHUUIDManager
 
 : NSObject
+(void)saveUUID; //儲存UUID

+(id)readUUID; //獲取UUID

+(void)deleteUUID; //刪除
@end


#import "LHUUIDManager.h"
#import "LHKeyChain.h"

@implementation LHUUIDManager : NSObject 
static NSString * const KEY_IN_KEYCHAIN = @"KEY_IN_KEYCHAIN";
static NSString * const KEY_IN_UUID = @"KEY_IN_UUID";

+(void
 
)saveUUID
{
    NSMutableDictionary *myUUIDDic = [NSMutableDictionary dictionary];
    [myUUIDDic setObject:[self creatUUID] forKey:KEY_IN_UUID];
    [LHKeyChain save:KEY_IN_KEYCHAIN data:myUUIDDic];
}

+(id)readUUID
{
    NSMutableDictionary *myUUIDDic = (NSMutableDictionary *)[LHKeyChain read:KEY_IN_KEYCHAIN];
    return [myUUIDDic objectForKey:KEY_IN_UUID];
}

+(void)deleteUUID
{
    [LHKeyChain lhDelete:KEY_IN_KEYCHAIN];
}

+(NSString *)creatUUID
{
    CFUUIDRef myUUID = CFUUIDCreate( nil );
    CFStringRef uuidString = CFUUIDCreateString( nil, myUUID );
    NSString * result = (NSString *)CFBridgingRelease(CFStringCreateCopy( NULL, uuidString));
    return result;
}
@end

#import <Foundation/Foundation.h>

@interface LHKeyChain : NSObject
+ (NSMutableDictionary *)getKeychain:(NSString *)keyChain ;

+ (void)save:(NSString *)keyChain data:(id)data;

+ (id)read:(NSString *)keyChain;

+ (void)lhDelete:(NSString *)keyChain;
@end





#import "LHKeyChain.h"

@implementation LHKeyChain
+ (NSMutableDictionary *)getKeychain:(NSString *)keyChain {
    return [NSMutableDictionary dictionaryWithObjectsAndKeys:
            (__bridge_transfer id)kSecClassGenericPassword,(__bridge_transfer id)kSecClass,
            keyChain, (__bridge_transfer id)kSecAttrService,
            keyChain, (__bridge_transfer id)kSecAttrAccount,
            (__bridge_transfer id)kSecAttrAccessibleAfterFirstUnlock,(__bridge_transfer id)kSecAttrAccessible,
            nil];
}

+ (void)save:(NSString *)keyChain data:(id)data {
    //Get search dictionary
    NSMutableDictionary *keychainQuery = [self getKeychain:keyChain];
    //Delete old item before add new item
    CFDictionaryRef aRef = (__bridge_retained CFDictionaryRef)keychainQuery;
    SecItemDelete(aRef);
    //Add new object to search dictionary(Attention:the data format)
    [keychainQuery setObject:[NSKeyedArchiver archivedDataWithRootObject:data] forKey:(__bridge_transfer id)kSecValueData];
    //Add item to keychain with the search dictionary
    SecItemAdd(aRef, NULL);
}

+ (id)read:(NSString *)keyChain {
    id ret = nil;
    NSMutableDictionary *keychainQuery = [self getKeychain:keyChain];
    //Configure the search setting
    [keychainQuery setObject:(id)kCFBooleanTrue forKey:(__bridge_transfer id)kSecReturnData];
    [keychainQuery setObject:(__bridge_transfer id)kSecMatchLimitOne forKey:(__bridge_transfer id)kSecMatchLimit];
    CFDataRef keyData = NULL;
    if (SecItemCopyMatching((__bridge_retained CFDictionaryRef)keychainQuery, (CFTypeRef *)&keyData) == noErr) {
        @try {
            ret = [NSKeyedUnarchiver unarchiveObjectWithData:(__bridge_transfer NSData *)keyData];
        } @catch (NSException *e) {
            NSLog(@"Unarchive of %@ failed: %@", keyChain, e);
        } @finally {
        }
    }
    return ret;
}

+ (void)lhDelete:(NSString *)keyChain {
    NSMutableDictionary *keychainQuery = [self getKeychain:keyChain];
    SecItemDelete((__bridge_retained CFDictionaryRef)keychainQuery);
}
@end

到這裡是所有關鍵程式碼，放上下載地址：點選下載

最後，忘了件重要的事情，要在xcode中啟用KeyChain：

當顯示為ON的時候才能使用KeyChain。