ALAssetPropertyDate returns “wrong” date

Question

I\'m currently working on a project in which i need to read some (Latitude, Longitude and date ) EXIF data. The location data seems correct, but the date i\'m getting seems to b

Answer 1

You can also get Exif DateTimeOriginal through ALAsset.

NSDateFormatter *dateFormatter = [[NSDateFormatter new] autorelease];
dateFormatter.dateFormat = @"y:MM:dd HH:mm:ss";
NSDate *date = [dateFormatter dateFromString:[[[[asset defaultRepresentation] metadata] objectForKey:@"{Exif}"] objectForKey:@"DateTimeOriginal"]];

Getting metadata from asset requires to load Exif header on memory (or entire image file?) and those methods above seems to use autorelease pool for the memory spaces. This may cause memory shortage or worse crash if you do a batch process for thousands of images.

To work around for memory shortage, you may use Ad-Hoc autorelease pool.

NSDateFormatter *dateFormatter = [[NSDateFormatter new] autorelease];
dateFormatter.dateFormat = @"y:MM:dd HH:mm:ss";
for (ALAsset *asset in thousandsOfAssets) {
    NSAutoreleasePool *pool = [NSAutoreleasePool new];
    NSDate *date = [dateFormatter dateFromString:[[[[asset defaultRepresentation] metadata] objectForKey:@"{Exif}"] objectForKey:@"DateTimeOriginal"]];
    // do something
    [pool release];
}

EDIT: correct wrong dateFormat (SS -> ss). Thanks @code-roadie

Answer 2

Though it's not explicitly documented, I'm guessing that this is the expected behavior. The date refers to when the asset was created and when you're modifying the image, you're probably implicitly creating a new asset. Nothing in the ALAsset documentation suggests that its properties correspond to the image's EXIF data.

To access the EXIF data, you could use the Image I/O framework (available since iOS 4.0), specifically the CGImageSourceCopyProperties function.