Giving View Controllers Access to the Image Store

The DetailViewController needs an instance of ImageStore to fetch and store images. You will inject this dependency into the DetailViewController’s designated initializer, just as you did for ItemsViewController and ItemStore in Chapter 10.

In DetailViewController.swift, add a property for an ImageStore. 

var item: Item! {
    didSet {
        navigationItem.title = item.name
    }
}
var imageStore: ImageStore!

Now do the same in ItemsViewController.swift. 

var itemStore: ItemStore!
var imageStore: ImageStore!

Next, still in ItemsViewController.swift, update prepare(for:sender:) to set the imageStore property on DetailViewController. 

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    // If the triggered segue is the "showItem" segue"
    switch segue.identifier {
    case "showItem"?:
        // Figure out which row was just tapped
        if let row = tableView.indexPathForSelectedRow?.row {

            // Get the item associated with this row and pass it along
            let item = itemStore.allItems[row]
            let detailViewController
                    = segue.destination as! DetailViewController
            detailViewController.item = item
            detailViewController.imageStore = imageStore
        }
    default:
        preconditionFailure("Unexpected segue identifier.")
    }
}

Finally, update AppDelegate.swift to create and inject the ImageStore. 

func application(_ application: UIApplication, didFinishLaunchingWithOptions
        launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    // Override point for customization after application launch.

    // Create an ItemStore
    let itemStore = ItemStore()

    // Create an ImageStore
    let imageStore = ImageStore()

    // Access the ItemsViewController and set its item store and image store
    let navController = window!.rootViewController as! UINavigationController
    let itemsController = navController.topViewController as! ItemsViewController
    itemsController.itemStore = itemStore
    itemsController.imageStore = imageStore
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