display image from URL retrieved from ALAsset in iPhone

Question

I am using a ALAsset Framework for accessing the files in the device's photo gallery.

So far I am able to access the thumbnail and display it.
I want to display the actual image in an image view but I am unable to figure out how to do this.

I tried using the URLs field in the ALAsset object but was unsuccessful.

Anybody knows how this can be done?

Here's some code where I was able to access the thumbnail and place it in a table cell:

- (UITableViewCell *)tableView:(UITableView *)tableView           cellForRowAtIndexPath:(NSIndexPath *)indexPath {     static NSString *CellIdentifier = @"Cell";    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];   if (cell == nil) {     cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];   }   //here 'asset' represents the ALAsset object     asset = [assets objectAtIndex:indexPath.row];        //i am accessing the thumbnail here   [cell.imageView setImage:[UIImage imageWithCGImage:[asset thumbnail]]];   [cell.textLabel setText:[NSString stringWithFormat:@"Photo %d", indexPath.row+1]];    return cell; } 

Answer 1

The API has changed the rules slightly and you dont get direct file system access to the iPhoto library any more. Instead you get asset library URL's like this.

assets-library://asset/asset.JPG?id=1000000003&ext=JPG

You use the ALAssetLibrary object to access the ALAsset object via the URL.

so from the docs for ALAssetLibrary throw this in a header (or your source)

typedef void (^ALAssetsLibraryAssetForURLResultBlock)(ALAsset *asset); typedef void (^ALAssetsLibraryAccessFailureBlock)(NSError *error); 

which isnt strictly needed but keeps things pretty.
and then in your source.

-(void)findLargeImage {     NSString *mediaurl = [self.node valueForKey:kVMMediaURL];      //     ALAssetsLibraryAssetForURLResultBlock resultblock = ^(ALAsset *myasset)     {         ALAssetRepresentation *rep = [myasset defaultRepresentation];         CGImageRef iref = [rep fullResolutionImage];         if (iref) {             largeimage = [UIImage imageWithCGImage:iref];             [largeimage retain];         }     };      //     ALAssetsLibraryAccessFailureBlock failureblock  = ^(NSError *myerror)     {         NSLog(@"booya, cant get image - %@",[myerror localizedDescription]);     };      if(mediaurl && [mediaurl length] && ![[mediaurl pathExtension] isEqualToString:AUDIO_EXTENSION])     {         [largeimage release];         NSURL *asseturl = [NSURL URLWithString:mediaurl];         ALAssetsLibrary* assetslibrary = [[[ALAssetsLibrary alloc] init] autorelease];         [assetslibrary assetForURL:asseturl                         resultBlock:resultblock                       failureBlock:failureblock];     } } 

A couple of things to note are that this uses blocks which were new to me before I started my iOS4 porting but you might like to look at

https://www.mikeash.com/pyblog/friday-qa-2008-12-26.html

and

https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/Blocks/Articles/00_Introduction.html

They bend your head a little but if you think of them as notification selectors or callbacks it kind of helps.

Also

• when findLargeImage returns the resultblock wont have run yet as its a callback. So largeImage wont be valid yet.
• largeImage needs to be an instance variable not scoped to the method.

I use this construct to do this when using the method but you may find something more suitable to your use.

[node.view findLargeImage]; UIImage *thumb = node.view.largeImage; if (thumb) { blah blah } 

Thats what I learned while trying to get this working anyway.

iOS 5 update

When the result block fires seems to be a bit slower with iOS5 & maybe single core devices so I couldnt rely on the image to be available directly after calling findLargeImage. So I changed it to call out to a delegate.

@protocol HiresImageDelegate <NSObject> @optional -(void)hiresImageAvailable:(UIImage *)aimage; @end 

and comme cá

//     ALAssetsLibraryAssetForURLResultBlock resultblock = ^(ALAsset *myasset)     {         ALAssetRepresentation *rep = [myasset defaultRepresentation];         CGImageRef iref = [rep fullResolutionImage];         if (iref) {             UIImage *largeimage = [UIImage imageWithCGImage:iref];             [delegate hiresImageAvailable:large];         }     };