How to get a photo's original filename in iOS?

Question

I'm currently developing an iPad app where a user will enter a photo filename in a text field (as part of field notes), then later they will import their photos to the iPad's photo library. The app will access the library using ALAssetsLibrary and enumerate over the photos, looking for ones with the filename they entered in their field notes. This would be the filename given to the photo by the camera that took it. For example "DSC_0019.JPG".

Is this not possible?

I noticed that if I import photos from my camera to iPad, then open iPhoto on my Mac and look at the iPad as a camera, I can "get info" on the images held on the iPad and see the original filename I'm looking for. However this is not contained in the metadata on the iPad.

Any help would be greatly appreciated.

Here is my code:

(In working with the CFDictionary, pretty much everything is null except the Exif keys which don't have what i'm looking for)

- (void)viewDidLoad
{
    [super viewDidLoad];

    //start activity animation
    [self.activity setHidden:NO];
    [self.activity startAnimating];

    //init our arrays
    autoAssignedAssets  = [[NSMutableArray alloc] init];
    unAssignedRecords   = [[NSMutableArray alloc] init];
    unAssignedAssets    = [[NSMutableArray alloc] init];

    //setup the library
    ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];



    //[ BLOCK ] => assetEnumerator
    //
    void (^assetEnumerator)(ALAsset *, NSUInteger, BOOL *) = ^(ALAsset *result, NSUInteger index, BOOL *stop) {

        if (result != nil) {

            if ([[result valueForProperty:ALAssetPropertyType] isEqualToString:ALAssetTypePhoto] ) {


                //=================================================================

                ALAssetRepresentation* representation = [result defaultRepresentation];

                // create a buffer to hold the data for the asset's image
                uint8_t *buffer = (Byte*)malloc(representation.size);// copy the data from the asset into the buffer
                NSUInteger length = [representation getBytes:buffer fromOffset: 0.0  length:representation.size error:nil];

                // convert the buffer into a NSData object, free the buffer after
                NSData *adata = [[NSData alloc] initWithBytesNoCopy:buffer length:representation.size freeWhenDone:YES];

                // setup a dictionary with a UTI hint.  The UTI hint identifies the type of image we are dealing with (ie. a jpeg, png, or a possible RAW file)
                // specify the source hint
                NSDictionary* sourceOptionsDict = [NSDictionary dictionaryWithObjectsAndKeys: (id)[representation UTI] ,kCGImageSourceTypeIdentifierHint, nil];


                // create a CGImageSource with the NSData.  A image source can contain x number of thumbnails and full images.
                CGImageSourceRef sourceRef = CGImageSourceCreateWithData((CFDataRef) adata,  (CFDictionaryRef) sourceOptionsDict);

                [adata release];

                CFDictionaryRef imagePropertiesDictionary;

                // get a copy of the image properties from the CGImageSourceRef
                imagePropertiesDictionary = CGImageSourceCopyPropertiesAtIndex(sourceRef,0, NULL);

                //NSString *imageFilename = (NSString*)CFDictionaryGetValue(imagePropertiesDictionary, kCGImagePropertyCIFFImageFileName);

                NSLog(@"%@", (NSDictionary *)CFDictionaryGetValue(imagePropertiesDictionary, kCGImagePropertyExifDictionary));

                CFNumberRef imageWidth = (CFNumberRef)CFDictionaryGetValue(imagePropertiesDictionary, kCGImagePropertyPixelWidth);
                CFNumberRef imageHeight = (CFNumberRef)CFDictionaryGetValue(imagePropertiesDictionary, kCGImagePropertyPixelHeight);

                int w = 0;
                int h = 0;

                CFNumberGetValue(imageWidth, kCFNumberIntType, &w);
                CFNumberGetValue(imageHeight, kCFNumberIntType, &h);

                // cleanup memory
                CFRelease(imagePropertiesDictionary);
                CFRelease(sourceRef);

                //NSLog(@"width: %d, height: %d", w, h);
                //NSLog(@"%@", imageFilename);



                //=================================================================


                //NSDictionary *metadata = [[result defaultRepresentation] metadata];
                //NSLog(@"\n\nAsset Info: %@", result);
                //NSLog(@"\n\n\n\nMetaData: %@", metadata);
                [autoAssignedAssets addObject:result];

            }//end if photo

        }//end if

    }; //end assetEnumerator block



    //[ BLOCK ] => assetGroupEnumerator
    //
    void (^assetGroupEnumerator)(ALAssetsGroup *, BOOL *) =  ^(ALAssetsGroup *group, BOOL *stop) {

        if(group != nil) {
            [group enumerateAssetsUsingBlock:assetEnumerator];
        }//end if


        //now we're done, reload and stop animations
        [self.tableView reloadData];
        [self.activity stopAnimating];
        [self.activity setHidden:YES];

    }; //end assetGroupEnumerator block



    //[ BLOCK ] => failureBlock
    //
    void (^failureBlock)(NSError *) = ^(NSError *error) {

        NSString *errorTitle = [error localizedDescription];
        NSString *errorMessage = [error localizedRecoverySuggestion];
        NSString *errorFailureDesc = [error localizedFailureReason];

        NSLog(@"Error: %@, Suggestion: %@, Failure desc: %@", errorTitle, errorMessage, errorFailureDesc);

    }; //end failureBlock




    //loop over all the albums and process the pictures with the blocks above
    [library enumerateGroupsWithTypes:ALAssetsGroupAll usingBlock:assetGroupEnumerator failureBlock: failureBlock];


}//end viewDidLoad

Answer 1

I was able to get an image's original filename like this:

NSString* originalFileName = [[asset defaultRepresentation] filename];

Answer 2

Extract the URL from the ALAsset, looks like this: assets-library://asset/asset.JPG?id=1000000001&ext=JPG

If you need different file names, make an internal-external paradigm:

#import <Foundation/Foundation.h>

@interface NSURL (NSURL_Asset)
- (NSURL*) toExternalForm;
- (NSURL*) fromExternalForm;
- (NSString*) toExternalFilename;    

@end

#import "NSURL+Asset.h"
#import "URLParser.h" // from http://iphone.demay-fr.net/2010/04/parsing-url-parameters-in-a-nsstring/

static NSString *const EXTERNAL_TOKEN = @"/assetExternalForm/";
@implementation NSURL (NSURL_Asset)

// assets-library://asset/asset.JPG/assetExternalForm/1000000001.JPG -> assets-library://asset/asset.JPG?id=1000000001&ext=JPG
- (NSURL*) fromExternalForm {
    if([self.scheme isEqualToString:@"assets-library"]) {
        NSRange slash = [self.absoluteString rangeOfString:EXTERNAL_TOKEN options:NSBackwardsSearch];
        if(slash.location != NSNotFound) {

            NSRange dot = [self.absoluteString rangeOfString:@"." options:NSBackwardsSearch];

            if(dot.location != NSNotFound) {
                NSString* extention = [self.absoluteString substringFromIndex:(dot.location + dot.length)];
                NSString* identifier = [self.absoluteString substringWithRange:NSMakeRange(slash.location + slash.length, dot.location - (slash.location + slash.length))];
                return [NSURL URLWithString:[NSString stringWithFormat:@"%@?id=%@&ext=%@", [self.absoluteString substringToIndex:slash.location], identifier, extention]];
            }
        }
    }
    return self;
}
// assets-library://asset/asset.JPG?id=1000000001&ext=JPG -> assets-library://asset/asset.JPG/assetExternalForm/1000000001.JPG
- (NSURL*) toExternalForm {
    if([self.scheme isEqualToString:@"assets-library"]) {
        NSRange range = [self.absoluteString rangeOfString:@"?"];
        if(range.location != NSNotFound) {
            URLParser *parser = [[[URLParser alloc] initWithURLString:self.absoluteString] autorelease];
            NSString* extention = [parser valueForVariable:@"ext"];
            NSString* identifier = [parser valueForVariable:@"id"];
            if(extention != NULL && identifier != NULL) {
                return [NSURL URLWithString:[NSString stringWithFormat:@"%@%@%@.%@", [self.absoluteString substringToIndex:range.location], EXTERNAL_TOKEN, identifier, extention]];
            }
        }
    }
    return self;
}
// assets-library://asset/asset.JPG?id=1000000001&ext=JPG -> 1000000001.JPG
- (NSString*) toExternalFilename {
    if([self.scheme isEqualToString:@"assets-library"]) {
        NSRange range = [self.absoluteString rangeOfString:@"?"];
        if(range.location != NSNotFound) {
            URLParser *parser = [[[URLParser alloc] initWithURLString:self.absoluteString] autorelease];
            NSString* extention = [parser valueForVariable:@"ext"];
            NSString* identifier = [parser valueForVariable:@"id"];

            if(extention != NULL && identifier != NULL) {
                return [NSString stringWithFormat:@"%@.%@", identifier, extention];
            }
        }
    }
    return NULL;
}
@end

Note that you do not need a filename to read the content of an ALAsset. Use the ALAsset.defaultRepresentation.getBytes method for that.