How do I avoid copying duplicate images to the iPhone Photo Library?

Question

Hello,

I am writing a simple application to copy a set of images to the user's photo library so that the user may use them as backgrounds. The problem is that if the user runs the application more than once, duplicate images will be copied to the photo library. Given the restrictions Apple places on accessing the contents of the photo library, what is the simplest way, if any, to avoid writing a duplicate file to the library?

Ben

Answer 1

You can store the images data that have been saved in your application by writing them to a file or using Core Data, that way you know which have been saved and which have not. Y

Answer 2

This answer is somewhat belated, but a late answer is better than no answer at all. The answer is that there is no way to check the photo library for a duplicate image (at least within the constraints of the public API). The only way to write to the photo library is via the UIKit global function:

void UIImageWriteToSavedPhotosAlbum ( UIImage *image, id completionTarget, SEL completionSelector, void *contextInfo );

which simply writes the instance of UIImage to the photo library. None of its four parameters represent an additional, potentially identifying, object that might be saved with the image. Nor does the UIImage or the CGImage it wraps provide a slot for "metadata" of this sort. Of course, one can always subclass, but unfortunately there is no way to inspect the contents of the PL. The PL is a write-only persistent store whose contents, at least as far as the API programmer is concerned, are essentially anonymous. Like a black hole, the photo library has a "one-way surface."