生成GUID

- (NSString *)generateUuidString

{

    CFUUIDRef uuid = CFUUIDCreate(kCFAllocatorDefault);

    

    NSString *uuidString = (NSString *)CFBridgingRelease(CFUUIDCreateString(kCFAllocatorDefault, uuid));

    

    CFRelease(uuid);

    

    return uuidString;

}