Classes/RootViewController.m

/*
     File: RootViewController.m
 Abstract: Main View Controller.
  Version: 1.1
 
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 */
 
#import "RootViewController.h"
#import "AlbumContentsViewController.h"
#import "AssetsDataIsInaccessibleViewController.h"
 
 
@interface RootViewController ()
 
@property (nonatomic, strong) ALAssetsLibrary *assetsLibrary;
@property (nonatomic, strong) NSMutableArray *groups;
 
@end
 
#pragma mark -
 
@implementation RootViewController
 
#pragma mark - View lifecycle
 
- (void)viewDidLoad {
    
    [super viewDidLoad];
 
    if (self.assetsLibrary == nil) {
        _assetsLibrary = [[ALAssetsLibrary alloc] init];
    }
    if (self.groups == nil) {
        _groups = [[NSMutableArray alloc] init];
    } else {
        [self.groups removeAllObjects];
    }
    
    // setup our failure view controller in case enumerateGroupsWithTypes fails
    ALAssetsLibraryAccessFailureBlock failureBlock = ^(NSError *error) {
 
        AssetsDataIsInaccessibleViewController *assetsDataInaccessibleViewController =
            [self.storyboard instantiateViewControllerWithIdentifier:@"inaccessibleViewController"];
        
        NSString *errorMessage = nil;
        switch ([error code]) {
            case ALAssetsLibraryAccessUserDeniedError:
            case ALAssetsLibraryAccessGloballyDeniedError:
                errorMessage = @"The user has declined access to it.";
                break;
            default:
                errorMessage = @"Reason unknown.";
                break;
        }
        
        assetsDataInaccessibleViewController.explanation = errorMessage;
        [self presentViewController:assetsDataInaccessibleViewController animated:NO completion:nil];
    };
    
    // emumerate through our groups and only add groups that contain photos
    ALAssetsLibraryGroupsEnumerationResultsBlock listGroupBlock = ^(ALAssetsGroup *group, BOOL *stop) {
        
        ALAssetsFilter *onlyPhotosFilter = [ALAssetsFilter allPhotos];
        [group setAssetsFilter:onlyPhotosFilter];
        if ([group numberOfAssets] > 0)
        {
            [self.groups addObject:group];
        }
        else
        {
            [self.tableView performSelectorOnMainThread:@selector(reloadData) withObject:nil waitUntilDone:NO];
        }
    };
    
    // enumerate only photos
    NSUInteger groupTypes = ALAssetsGroupAlbum | ALAssetsGroupEvent | ALAssetsGroupFaces | ALAssetsGroupSavedPhotos;
    [self.assetsLibrary enumerateGroupsWithTypes:groupTypes usingBlock:listGroupBlock failureBlock:failureBlock];
}
 
 
#pragma mark - UITableViewDataSource
 
// determine the number of rows in the table view
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    
    return self.groups.count;
}
 
// determine the appearance of table view cells
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    
    static NSString *CellIdentifier = @"Cell";
    
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
    
    ALAssetsGroup *groupForCell = self.groups[indexPath.row];
    CGImageRef posterImageRef = [groupForCell posterImage];
    UIImage *posterImage = [UIImage imageWithCGImage:posterImageRef];
    cell.imageView.image = posterImage;
    cell.textLabel.text = [groupForCell valueForProperty:ALAssetsGroupPropertyName];
    cell.detailTextLabel.text = [@(groupForCell.numberOfAssets) stringValue];
 
    return cell;
}
 
 
#pragma mark - Segue support
 
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    
    if ([[segue identifier] isEqualToString:@"showDetail"]) {
        NSIndexPath *selectedIndexPath = [self.tableView indexPathForSelectedRow];
        if (self.groups.count > (NSUInteger)selectedIndexPath.row) {
            
            // hand off the asset group (i.e. album) to the next view controller
            AlbumContentsViewController *albumContentsViewController = [segue destinationViewController];
            albumContentsViewController.assetsGroup = self.groups[selectedIndexPath.row];
        }
    }
}
 
@end