Chris Aves

Let’s assume for one moment the possibility that Alisto crashes, is terminated by iOS or indeed by the user. Wouldn’t it be nice to remember the most recently viewed List and pop that up on the screen when the application next launches?

Because a user navigates from a list of Lists, to an specific list, in this situation the application needs to push an additional view onto the stack when it launches. But, in the interests of tidyiness, I don’t want the main application delegate to do this work. This is how I’ve done it:

I want to store in NSUserDefaults a reference to the list currently on display, and whenever that changes the reference is updated. NSUserDefaults can only store simple objects, so storing an NSManagedObject is out of the question. However, each NSManagedObject does have a unique URL obtained via its URIRepresentation method.

The first step is to have the controller which displays a list to be record the list on display. This is achieved by updating the viewDidLoad method. As you’ll recall from previous posts, item is the actual list.

NSURL *url = [[item objectID] URIRepresentation];
[[NSUserDefaults standardUserDefaults] setURL:url forKey:[NSString stringWithFormat:@"%d", AlistoPrefCurrentListItemURI]];

The ListsViewController which is responsible for handling the list of lists can now show a list if it’s tapped on, or if commanded to on launch. It’s therefore appropriate to factor out the code which pushes the display of an individual list:

- (void)viewList:(ListItem *)item {
    if (item) {
        ListViewController *listViewController = [[ListViewController alloc] init];    
        [listViewController setItem:item];

        [[self navigationController] pushViewController:listViewController animated:YES];
    }
}

This is invoked either via the tableView:didSelectRowAtIndexPath method (as per usual) or (now) via the viewWillAppear method, which I updated as follows:

- (void)viewWillAppear:(BOOL)animated {    
    [super viewWillAppear:animated];
    [[self tableView] reloadData];

    if ([self pushedListItem]) {
        [self viewList:pushedListItem];
        pushedListItem = nil;
    }
}

pushListItem is a property which references a list object, it is intended to be set by the application delegate to indicate that a list is to be shown immediately. In the above code, as soon as the controller view appears, the controller examines the reference and pushes the list on display via the aforementioned viewList method.

The application delegate’s didFinishLaunchingWithOptions then has the following code which examines the user setting, converts the setting into an actual object, then tells the (just created) controller the list object it should show.

ListsViewController *listsViewController = [[ListsViewController alloc] init];
    
NSURL *url = [[NSUserDefaults standardUserDefaults] URLForKey:[NSString stringWithFormat:@"%d", AlistoPrefCurrentListItemURI]];
if (url) {
    NSError *anyError = nil;
    NSManagedObjectID *objectID = [[CACoreData sharedPersistentStoreCoordinator] managedObjectIDForURIRepresentation:url];
    ListItem *item = (ListItem *)[[CACoreData sharedManagedObjectContext] existingObjectWithID:objectID error:&anyError];
    if (item) {
        [listsViewController setPushedListItem:item];
    }
}