The Per Rewrite Diaries: Day 27

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.

Slow down and sleep

To test what unit type (if any) the list should be limited to, I changed the private _unitType property in the ProductList to

private(set) var unitType: Unit?

This value is set when the first ProductItem is added to the list. Then I can add it as a property with the same access level to the ProductDetailContentViewController:

protocol ProductDetailContentViewControllerDelegate: AnyObject {
    var numberOfProductItems: Int { get }
    // Other protocol stuff
}

This exposes it to the view controller’s subviews, but here’s something I was perplexed by. In the view controller’s viewDidLoad() method, I (via a call to a setupViews() method) instantiate a subview, and set its delegate. But when I was trying to access that delegate from within the subview’s initializer, it would return nil. It took me longer than I care to admit to realize that the delegate isn’t initialized until after my subview is:

//... other viewDidLoad() stuff in the view controller
productDetailFormView = new ProductDetailFormView(frame: .zero);
productDetailFormView.delegate = self

In retrospect, this is obvious. You’ve got to wait until the view’s initializer does its thing, and then the view’s delegate is set — so don’t try to access it in the view’s initializer.

What’s fascinating to me is that —while I know all this— it was incomprehensible why this was happening while I was in the thick of programming, until I gave up and took a break. Why? Probably because I had a lousy night’s sleep, and was rushing to get something done early this morning.

The takeaway: get a good night’s sleep, and don’t rush your work.

Tomorrow, I continue working on this.