Now that I am finally exporting with random file names I feel like I am on the home straight. But there is plenty more still to do: looking for problems, for instance.
There are two things that can go wrong with the export. First there could be an existing file in the folder I am exporting to. This is actually quite likely since repeated exports will create the same names for the same files unless the salt is changed.
To solve that I add some code to display an alert if the rename fails. I modify the call to movePath by adding a handler. If there is an error with the rename, the handler method will be called:
To support the handler, I added two methods:
I had to incorporate a workaround for a bug: the return value of fileManager:shouldProceedAfterError is actually ignored by movePath:toPath:. NO always comes back. So I had to create an ivar to pass that value.
Although this code handles errors just fine, there is a better way of dealing with the situation of existing files with the same name as new files. I can create all the random file names and make sure that none of them exist in the folder before I even start the export. That will ensure that errors are truly exceptional (cause by hardware or other programs maybe).
Another problem I may run into is that there may be too many files for the randomness. Exporting 1000 files with three random decimal digits in the name is guaranteed to run into trouble.
So my code needs to ensure that all of the random names are unique with respect to themselves and to the destination folder. The solution is to create dictionary of existing filenames with NSNull objects. I use a dictionary for finding duplicates because they are very efficient for large numbers of images:
To that I add the files being renamed, the difference being that the files being renamed are stored with the new random name. The case-insensitive nature of the filing system means that I need another another dictionary to track file names coerced to lower case. Collisions in that dictionary mean that I have a problem.
My renaming code ignores the existing files by looking for the NSNulls and renames the rest:
The other parts of this series can be found via the Cocoa page.
