- (NSString*) getUUID
{
    // initialize keychaing item for saving UUID.
    KeychainItemWrapper *wrapper = [[KeychainItemWrapper alloc] initWithIdentifier:@"UUID" accessGroup:nil];
    NSString *uuid = [wrapper objectForKey:(__bridge id)(kSecAttrAccount)];
    if( uuid == nil || uuid.length == 0)
    {
        // if there is not UUID in keychain, make UUID and save it.
        CFUUIDRef uuidRef = CFUUIDCreate(NULL);
        CFStringRef uuidStringRef = CFUUIDCreateString(NULL, uuidRef);
        CFRelease(uuidRef);
        uuid = [NSString stringWithString:(__bridge NSString *) uuidStringRef];
        CFRelease(uuidStringRef);
         // save UUID in keychain
        [wrapper setObject:uuid forKey:(__bridge id)(kSecAttrAccount)];
    }
    return uuid;
}


#import "ViewController.h"
#import "KeychainItemWrapper.h"

@interface ViewController ()

@end

@implementation ViewController

//uuid 생성 및 리턴하는 함수
- (NSString*) getAPInfo
{
    //uuid 저장하기 위해서 키 체이닝 생성 및 초기화
    KeychainItemWrapper *wrapper = [[KeychainItemWrapper alloc] initWithIdentifier:@"UUID" accessGroup:nil];

    NSString *uuid = [wrapper objectForKey:(__bridge id)(kSecAttrAccount)];

    if( uuid == nil || uuid.length == 0)
    {
        //키체인에 uuid 없으면 만들어서 저장
        CFUUIDRef uuidRef = CFUUIDCreate(NULL);
        CFStringRef uuidStringRef = CFUUIDCreateString(NULL, uuidRef);
        CFRelease(uuidRef);
        uuid = [NSString stringWithString:(__bridge NSString *) uuidStringRef];
        CFRelease(uuidStringRef);

        // 키체인에 uuid 저장
        [wrapper setObject:uuid forKey:(__bridge id)(kSecAttrAccount)];

    }

    return uuid;

}

//화면이 로딩될때 호출된다
- (void)viewDidLoad {
    [super viewDidLoad];
    //uuid 호출
    NSString *uuid = [self getAPInfo];
    NSLog(@"uuid 값: %@" , uuid);
}


- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}


@end
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