EXC_BAD_ACCESS error using ALAssetsLibrary assetForURL:resultBlock:failureBlock: - objective-c

Question

I'm trying to read the EXIF data from an image, selected by a user. I'm using the ALAssetLibrary for this. So far I've managed to get the reference URL needed for the assetForURL:resultBlock:failureBlock: method, but when I try to do anything with the reference URL i get a EXC_BAD_ACCESS error.
An NSLog of the URL, right before using it, results in the (correct, as far as i know) string:
assets-library://asset/asset.JPG?id=1000000003&ext=JPG
I've been trying to figure this out, but I seem to be hitting a dead end each time. I must admit I'm new to Objective-C in general, so please feel free to criticize my code accordingly.
Code (far from the complete classes, but i think it should be sufficient):
//Class_X.m
-(void)readExifDataFromSelectedImage:(NSURL *)imageRefURL
{
void (^ALAssetsLibraryAssetForURLResultBlock)(ALAsset *) = ^(ALAsset *asset)
{
NSLog(#"Test:Succes");
};
ALAssetsLibrary *myAssetLib;
NSLog(#"%#",imageRefURL);
[myAssetLib assetForURL:imageRefURL
resultBlock:ALAssetsLibraryAssetForURLResultBlock
failureBlock:^(NSError *error){NSLog(#"test:Fail");}];
}
//Class_Y.m
//This also conforms to the UIImagePickerControllerDelegate And the NavigationControllerDelegate protocols:
- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
self.referenceURL = [info valueForKey:#"UIImagePickerControllerReferenceURL"];
NSString *mediaType = [info
objectForKey:UIImagePickerControllerMediaType];
[self dismissModalViewControllerAnimated:YES];
if ([mediaType isEqualToString:(NSString *)kUTTypeImage]) {
UIImage *selectedImage = [info objectForKey:UIImagePickerControllerOriginalImage];
imageView.image = selectedImage;
btnNoPicture.hidden = YES;
btnSelectPicture.hidden = YES;
btnTakePicture.hidden = YES;
imageView.hidden = NO;
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:#"Use this image?"
message:#"Are you sure you want to use this image?"
delegate:self
cancelButtonTitle:#"No"
otherButtonTitles:#"Yes", nil];
[alert show];
[alert release];
}
}
-(void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{
if (buttonIndex == 0)
{
//Do not use the selected image.
imageView.image = nil;
imageView.hidden = YES;
//Restart picking process
}
else
{
// I have an instance variable of type Class_X which i use
// throughout this class; let's call this variable "report".
// I also have the referenceURL stored as an instance variable.
[self.report readExifDataFromSelectedImage:self.referenceURL];
}
}

Answer 1

EXC_BAD_ACCESS is most often the result of an over-released object (dangling pointer). As the library operates asynchronously, your block is executed after the readExifDataFromSelectedImage: method has returned, so imageRefURL is probably already deallocated at this point. Try to retain the URL before requesting the asset and release it in the success and failure blocks.