How can the filename be extracted from an ALAsset?
Is there a way to get this via the url or some other way?
Asked
Active
Viewed 1.2k times
2 Answers
33
From iOS 5.0 you can get the file from ALAssetRepresentation Class.
ALAssetRepresentation *rep = [anAssetItem defaultRepresentation];
NSString *fileName = [rep filename];
Seunghoon
- 5,632
- 5
- 35
- 41
5
Update: As yeonsh notes below, from iOS 5.0 there is a better way. This answer is relevant for iOS < 5.0.
You can extract an URL from the ALAsset, but all the filenames are the same, on the form
assets-library://asset/asset.JPG?id=1000000001&ext=JPG
If you for some reason need different file names, try making 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.
-
@Thomas: I need the filenames for adding multiple images to an email as attachments. How would these filenames be accessed via the ALAssets? thanks – some_id Feb 19 '11 at 16:32
-
Well the MFMailComposeViewController.addAttachmentData method needs the NSData of the ALAsset, and then 'any' filename and the mimeType. So I would modify the toExternalForm method above to just return the filename, e.g.'1000000001.JPG', and make a method which maps from filename extension to mimeType, '.JPG' to -> image/jpeg. – ThomasRS Feb 19 '11 at 17:30
-
@Thomas: How should this be used? Can I just use the toExternalForm method in my current class or what is the @implementation NSURL for? If I can use it in my current class(just the method), what is self.scheme? Thanks a lot. – some_id Feb 20 '11 at 00:29
-
No real magic tricks, copy the method to whatever class you want. The @implementation NSURL is just for extending the NSURL class for those pieces of code whom want to import that header / add those methods to NSURL, sort of a 'utility' extension for NSURL. Yeah so this is kind of a clean approach, with the right setup, i.e. import, you can make calls to NSURL with in the above methods :P – ThomasRS Feb 20 '11 at 08:10
-
@Thomas: Thanks for all the help, I have an issue that URLParser doesnt exist, when importing(both imports dont exist). Is there a framework I should add? Also "EXTERNAL_TOKEN" doesnt exist. – some_id Feb 20 '11 at 10:56
-
EXTERNAL_TOKEN does exist, see the above code? And see http://iphone.demay-fr.net/2010/04/parsing-url-parameters-in-a-nsstring/. – ThomasRS Feb 20 '11 at 17:43
-
My bad. Thanks. So what is this used on? If I want to get the filename? What calls this function. Sorry for all the questions, I am just not sure how to use this, and no one else seems to know. – some_id Feb 20 '11 at 21:50
-
Modify the NSURL URLWithString method to change what is returned. – ThomasRS Feb 20 '11 at 22:28
-
@Thomas: I really need your help with this. I read the link, but am still unsure how to even use this. What would call it or how do I get the filename. your my only hope. No one else can answer this. – some_id Feb 21 '11 at 13:14
-
That seems to work thanks. it extracts the filename, but doesnt display the image . i get the print out "the image in mail for loop index:0 is 1000000002.JPG" – some_id Feb 22 '11 at 09:18
-
search this site if you have problems with mail, if you find nothing then start a new question with a good and understandable description of your problem. – ThomasRS Feb 22 '11 at 15:15