Question

I am retrieving an image from the user’s photo library, and saving that image in the documents directory. I am currently naming the picture based on what the user enters in a text field. This works, but the text field is not really a good name for the picture. I would like to use some sort of unique identifier for naming the pictures.

Any ideas or suggestions? I just do not want to have conflicts when a large amount of photos are saved by the user.

Answer 1

One method is to use UUIDs. Here is an example:

// return a new autoreleased UUID string
- (NSString *)generateUuidString
{
  // create a new UUID which you own
  CFUUIDRef uuid = CFUUIDCreate(kCFAllocatorDefault);

  // create a new CFStringRef (toll-free bridged to NSString)
  // that you own
  NSString *uuidString = (NSString *)CFUUIDCreateString(kCFAllocatorDefault, uuid);

  // transfer ownership of the string
  // to the autorelease pool
  [uuidString autorelease];

  // release the UUID
  CFRelease(uuid);

  return uuidString;
}

Or an ARC version:

// Create universally unique identifier (object)
CFUUIDRef uuidObject = CFUUIDCreate(kCFAllocatorDefault);

// Get the string representation of CFUUID object.
NSString *uuidStr = (__bridge_transfer NSString *)CFUUIDCreateString(kCFAllocatorDefault, uuidObject);
CFRelease(uuidObject);

Even easier iOS6+ solution:

NSString *UUID = [[NSUUID UUID] UUIDString];

More info here: http://blog.ablepear.com/2010/09/creating-guid-or-uuid-in-objective-c.html and here: http://en.wikipedia.org/wiki/Universally_unique_identifier