Question

If I for example do this:

NSDirectoryEnumerator *directoryEnumerator = [[NSFileManager defaultManager] enumeratorAtURL:cacheDirectory
                                                                  includingPropertiesForKeys:@[NSURLContentAccessDateKey]
                                                                                     options:NSDirectoryEnumerationSkipsHiddenFiles
                                                                                errorHandler:nil];

NSURL *fileURL;
while (fileURL = [directoryEnumerator nextObject])
{
    NSDate *fileDate;
    [fileURL getResourceValue:&fileDate forKey:NSURLContentAccessDateKey error:nil];

    if ([cacheDate compare:fileDate] == NSOrderedDescending) // Delete all files with access date older then cacheDate(defined elsewhere)
        [[NSFileManager defaultManager] removeItemAtURL:fileURL error:nil];
}

Can the directory enumerator get “corrupted”, for example can I get unexpected results, because index of each file changes?

I would however like to use the enumeratorAtURL method and not contentsOfDirectoryAtURL because I have to deal with large amount of files (more then 100,000). So contentsOfDirectoryAtURL takes a lot of memory.

Answer 1

It’s generally a bad idea to remove items from a container while iterating through it.

You could save all fileURLs that you want to delete in an array and then iterate through the array to delete the files.

Something like this:

NSMutableArray *urlsToDelete = [[NSMutableArray alloc] init];

NSDirectoryEnumerator *directoryEnumerator = [[NSFileManager defaultManager] enumeratorAtURL:cacheDirectory
                                                                  includingPropertiesForKeys:@[NSURLContentAccessDateKey]
                                                                                     options:NSDirectoryEnumerationSkipsHiddenFiles
                                                                                errorHandler:nil];

NSURL *fileURL;
while (fileURL = [directoryEnumerator nextObject])
{
    NSDate *fileDate;
    [fileURL getResourceValue:&fileDate forKey:NSURLContentAccessDateKey error:nil];

    if ([cacheDate compare:fileDate] == NSOrderedDescending) // Delete all files with access date older then cacheDate(defined elsewhere)
        [urlsToDelete addObject:fileURL];
}

for (NSURL *fileURL in urlsToDelete) {
     [[NSFileManager defaultManager] removeItemAtURL:fileURL error:nil];
}