Iphone: unable to show photos using AlAssetsLibrary - iphone

Question

I currently sending ipa to friends for testing. Funny thing is, one of my tester able view her photos stored on her phone which was running IOS 5 using iPhone 4.
Another 2 testers: one has iPhone 4 (IOS 4.3.3) , and iPhone 3GS (IOS 5.0.1) both of them can't see photos stored on their phone.
These are the code I have used:
ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
void (^assetEnumerator)(ALAsset *, NSUInteger, BOOL *) = ^(ALAsset *result, NSUInteger index, BOOL *stop) {
if(result != NULL) {
//NSLog(#"See Asset: %#", #"ggg");
[assets addObject:result];
}
};
NSLog(#"location = %i length = %i ", range->location, range->length );
void (^assetGroupEnumerator)(ALAssetsGroup *, BOOL *) = ^(ALAssetsGroup *group, BOOL *stop) {
if(group != nil) {
NSRange *datarange = malloc(sizeof(NSRange));
range->total = [group numberOfAssets];
datarange->location = [group numberOfAssets] - range->location - range->length;
datarange->length = range->length;
NSLog(#" total = %i", range->total);
int location = [group numberOfAssets] - range->location - range->length;
if (location < 0)
{
datarange->location = 0;
datarange->length = [group numberOfAssets] - range->location;
}
NSIndexSet *indexset = [ [NSIndexSet alloc] initWithIndexesInRange:*datarange];
[group enumerateAssetsAtIndexes:indexset options:NULL
usingBlock:assetEnumerator];
[indexset release];
free(datarange);
[self loadAssetToScrollView:assets];
}
};
[assets release];
assets = [[NSMutableArray alloc] init];
[library enumerateGroupsWithTypes:ALAssetsGroupSavedPhotos
usingBlock:assetGroupEnumerator
failureBlock: ^(NSError *error) {
NSLog(#"Failure");
}];
[library release];
I saw somebody say about asynchronous thing in some other threads but don't know is it the case. He say put dispatch_async in the enumerate group block.
Does anyone know what is wrong.
Additionally, one of tester with iOS 4.3.3 can show his photos after enabling location services under General->Setting. Why we have to enable it? Can we enabled it on code since it will be quite disturbing to the user who using our application.

Answer 1

Also on iOS 5.x you must retain your ALAssetsLibrary instance so long as you need to work with the collected assets. When you release your ALAssetsLibrary instance like in your code just after calling [library enumerateGroupsWithTypes:…] all the collected assets will be invalid.
See also the ALAssetsLibrary doc - overview:
"… The lifetimes of objects you get back from a library instance are tied to the lifetime of the library instance. …"

Answer 2

Yes, it is incredibly frustrating, but that is how it is, and you cannot enable location services in code (that is a good thing though).

Answer 3

I would move the first block ^assetGroupEnumerator to the heap by [[<#block#> copy] autorelease]. Why? Because this block would be autoreleased by the runloop, if there are many assets need to be enumerated through.

Answer 4

One more thing: don't use [self loadAssetToScrollView:assets]; inside the block but get the weak reference of self before the block like this:
__block YourExampleClassInstance *weakSelf = self;
and further use this weakSelf instance inside the block:
[weakSelf loadAssetToScrollView:assets];
void (^assetGroupEnumerator)… = ^(ALAssetsGroup *group, BOOL *stop) {
…
};
Why? To avoid retain cycles.