iOS - Iteration in some folders - ios

Question

I need to get some files in definite folders. For this purpose I use this answer and it works fine. However, my folder structure is like:
Documents/
idOfFolder1/
images/
image1.jpg
image2.png
sounds/
sound1.mp3
files/
file1.pdf
idOfFolder2/
images/
...
I need to iterate through all folders having a specific id and get images. Since the answer written iterates through all folders it takes much more time than normal (we have many files). To optimize process, I want to skip "sounds" and "files" folders. Is there a way to handle this?
Thank you!

Answer 1

If you don't like to use NSPredicate, following code will also do what you want,
(this code will directly access the folders with given ids and pick everything inside the images folders)
-(void) printImagesOfFolders:(NSArray *) folderIds{
for(NSString *folderId in folderIds){
NSArray *paths = [[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask];
NSURL *documentsURL = [paths lastObject];
NSString * imageFolderPath = [NSString stringWithFormat:#"%#/images", folderId];
NSURL *rootURL = [documentsURL URLByAppendingPathComponent:imageFolderPath];
NSFileManager *fm = [NSFileManager defaultManager];
NSDirectoryEnumerator *dirEnumerator = [fm enumeratorAtURL:rootURL
includingPropertiesForKeys:#[NSURLNameKey, NSURLIsDirectoryKey]
options:NSDirectoryEnumerationSkipsHiddenFiles
errorHandler:nil];
for (NSURL *url in dirEnumerator) {
NSLog(#"url: %#", url);
}
}
}
How to use it
[self printImagesOfFolders:#[#"idOfFolder1",#"idOfFolder2",#"idOfFolder3",#"idOfFolder4"]];

Answer 2

I think you can implement it in a such different way using a NSPredicate onto the NSDirectoryEnumerator array as in this answer Iterating through files in nested folders or Filter NSFileManager with NSPredicate but the syntax can be awkward: take a look at NSPredicate syntax documentation NSPredicate Format String
In your case I would either:
1. use fast enumeration with a for loop
2. if possible redesign the folder structures
3. use core data or another caching system to speed up the loading process (this involves to sync time to time with the real files)

Answer 3

That's right. The upstairs is right, and the index will be named directly based on the picture so that CPU can find the files accurately