在开发过程中，很多时候需要查看该用户是上传唯一识别标志，安卓设备可以设定上传IMEI。但苹果设备已经不支持获取IMEI,作为替代我们使用UUID来作唯一标示符。
****一、uuid类和keychain类****

#import <Foundation/Foundation.h>

@interface HAUUID : NSObject
/**
 *  获取uuid
 *
 *  @param block 返回uuid和是否初装
 */
+ (void)getUUIDCompletionBlock:(void(^)(NSString*UUIDString,BOOL firstInstall))block;
@end

#import "HAUUID.h"
#import "HAKeyChainStore.h"

#define  KEY_USERNAME_PASSWORD @""
#define  KEY_USERNAME @"com.company.app.username"
#define  KEY_PASSWORD @"com.company.app.password"
@implementation HAUUID
+ (void)getUUIDCompletionBlock:(void(^)(NSString*UUIDString,BOOL firstInstall))block{
    NSString * strUUID = (NSString *)[HAKeyChainStore load:KEY_USERNAME_PASSWORD];
    BOOL installState  =NO;
    //首次执行该方法时，uuid为空
    if ([strUUID isEqualToString:@""] || !strUUID)
    {
        installState =YES;//初装
        //生成一个uuid的方法
        CFUUIDRef uuidRef = CFUUIDCreate(kCFAllocatorDefault);
        
        strUUID = (NSString *)CFBridgingRelease(CFUUIDCreateString (kCFAllocatorDefault,uuidRef));
        
        //将该uuid保存到keychain
        [HAKeyChainStore save:KEY_USERNAME_PASSWORD data:strUUID];
        
    }
    block(strUUID,installState);
}


@end

#import <Foundation/Foundation.h>

@interface HAKeyChainStore : NSObject

+ (void)save:(NSString *)service data:(id)data;
+ (id)load:(NSString *)service;
+ (void)deleteKeyData:(NSString *)service;

@end

#import "HAKeyChainStore.h"

@implementation HAKeyChainStore


+ (NSMutableDictionary *)getKeychainQuery:(NSString *)service {
    return [NSMutableDictionary dictionaryWithObjectsAndKeys:
            (id)kSecClassGenericPassword,(id)kSecClass,
            service, (id)kSecAttrService,
            service, (id)kSecAttrAccount,
            (id)kSecAttrAccessibleAfterFirstUnlock,(id)kSecAttrAccessible,
            nil];
}

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

+ (id)load:(NSString *)service {
    id ret = nil;
    NSMutableDictionary *keychainQuery = [self getKeychainQuery:service];
    //Configure the search setting
    //Since in our simple case we are expecting only a single attribute to be returned (the password) we can set the attribute kSecReturnData to kCFBooleanTrue
    [keychainQuery setObject:(id)kCFBooleanTrue forKey:(id)kSecReturnData];
    [keychainQuery setObject:(id)kSecMatchLimitOne forKey:(id)kSecMatchLimit];
    CFDataRef keyData = NULL;
    if (SecItemCopyMatching((CFDictionaryRef)keychainQuery, (CFTypeRef *)&keyData) == noErr) {
        @try {
            ret = [NSKeyedUnarchiver unarchiveObjectWithData:(__bridge NSData *)keyData];
        } @catch (NSException *e) {
            NSLog(@"Unarchive of %@ failed: %@", service, e);
        } @finally {
        }
    }
    if (keyData)
        CFRelease(keyData);
    return ret;
}



+ (void)deleteKeyData:(NSString *)service {
    NSMutableDictionary *keychainQuery = [self getKeychainQuery:service];
    SecItemDelete((CFDictionaryRef)keychainQuery);
}

@end

****二、生成Entitlements文件****

左侧的目录会自动生成Entitlements文件，不需要自己创建了。
也就是说，Bundle Identifier、Keychain Sharing的Keychain Groups、Entitlements文件的Keychain Access Groups的第一个元素，它们要保持上图所示的一致性。