The Per Rewrite Diary: Day 9

This post is part of a series about rewriting my iOS app, Per. Per is a price per unit comparison app with a bunch of neat convenience figures, but it hasn’t been updated in years, so I’m rewriting it from scratch to eliminate a bunch of technical debt. Just because it’s not an open-source app doesn’t mean I can’t share what I learn as I go!

See the rest of the series here.

Delegate, Delegate, Delegate

So I’m now working on a simple UI to add product details to the table view. Presenting a new product detail content view controller from the product list context view controller isn’t too hard — when the ➕ button is tapped in the navigation bar, we just need to responding by pushing a new view controller onto the navigation stack:

@objc func handleAddProductBarButtonItemTapped(sender: UIBarButtonItem) {
    let productDetailVC = ProductDetailContentViewController()
    self.present(productDetailVC, animated: true, completion: nil)
}

But we also need to be able to add a item to the product list, so we create a delegate property in this new product detail content view controller:

weak var delegate: ProductListContextViewController!

The tells the detail VC, “hey, delegate any work back to the product list context VC”; in this case, Per will collect the details of the new product you want to add in the ProductDetailContentViewController and pass them back when to its delegate when you tap an “Add” button:

@objc func addButtonTapped(_ sender: UIButton!) {
    delegate.add(createRandomProduct())
    self.dismiss(animated: true, completion: nil)
}

(I’ve just got a placeholder “Add” button that calls the createRandomProduct() method I mentioned on day 7).

Now, I can go back to the product list context view controller and add itself as a delegate to the product detail content view controller:

@objc func handleAddProductBarButtonItemTapped(sender: UIBarButtonItem) {
    let productDetailVC = ProductDetailContentViewController()
    productDetailVC.delegate = self
    self.present(productDetailVC, animated: true, completion: nil)
}

And we add the method called:

func add(_ item: ProductItem) {
    self.contentViewController.productList.add(item, sort: true)
    self.contentViewController.loadView()
}

So, to summarize, here’s what happens:

  • The ProductListContextViewController creates a ProductDetailContentViewController and tells it, “hey, I’m your delegate!” before presenting it.
  • The ProductDetailContentViewController presents a UI for collecting product info (price, quantity, units), and then calls the add() method of its delegate (the ProductListContextViewController) before dismissing itself.
  • The ProductListContextViewController receives the call to its add() method and updates the product list and table view accordingly.

There’s something weird about how my detail view controller dismisses itself, though — sometimes it’s a smooth animation, and sometimes it just disappears. I’ll figure out why tomorrow.

Angelo Stavrow

Montreal, Canada
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Tinkerer with a strong interest for development, of both the personal and software persuasion; easily defeated with spatulas. Equal measures enthusiasm and concern for tech's effect on the world. He/him.