Every once in a while I look at a feature in Swift and I fall down a rabbit hole to explore it so I can eventually write about it. The OptionSet protocol is one of these Swift features. If you've ever written an animation and passed it a list of options like this, you have already used OptionSet: UIView.animate( withDuration: 0.6, delay: 0, options: [.allowUserInteraction, .curveEaseIn], animations: { myView.layer.opacity = 0 }, completion: { _ in }) You may not have realized that you weren't passing an array to the options parameter, and that's not surprising. After all, the options...

When you've added Core Data to your SwiftUI project and you have some data stored in your database, the next hurdle is to somehow fetch that data from your Core Data store and present it to the user. In this week's post, I will present two different ways that you can use to retrieve data from Core Data and present it in your SwiftUI application. By the end of this post you will be able to: Fetch data using the @FetchRequest property wrapper Expose data to your SwiftUI views with an observable object and an @Published property. Since @FetchRequest is...

If you've ever wanted to decode a bunch of JSON data into NSManagedObject instances you've probably noticed that this isn't a straightforward exercise. With plain structs, you can conform your struct to Codable and you convert the struct from and to JSON data automatically. For an NSManagedObject subclass it's not that easy. If your Core Data data model is configured to automatically generate your entity class definitions for you (which is the default), you may have tried to write the following code to conform your managed object to Decodable: extension MyManagedObject: Decodable { } If you do this, the compiler...

Unit testing is an important skill in the toolbox of any engineer. Knowing how to write a reliable, robust test suite helps you write reliable and robust code. If you've followed my introduction to unit testing part one and part two, or if you're experienced with unit testing you know that your tests should run isolated from any other tests. You also know that you should make sure that your test relies on as few external dependencies as possible. When you want to test your Core Data code, it might not be immediately obvious how you can test your Core...

In Xcode 12 you can create projects that no longer use an AppDelegate and SceneDelegate to manage the application lifecycle. Instead, we can use Swift's new @main annotation to turn a struct that conforms to the App protocol into the main entry point for our applications. When you create a new project in Xcode 12, you have the option to use the SwiftUI App application lifecycle for your SwiftUI project. While Xcode 12 beta 5 introduces an option to include Core Data in your SwiftUI application when you create a new project, you might have an existing SwiftUI project that...

As developers, we constantly deal with layers of abstractions that make our lives easier. We have abstractions over low level networking operations that allow us to make network calls with URLSession. Core Data provides an abstraction over data persistence that can be used to store information in an sqlite database. And there are many, many more abstractions that we all use every day. Over the past few weeks I have seen many people ask about using Core Data in pure SwiftUI projects created in Xcode 12. These projects no longer require an App- and SceneDelegate, and the checkbox to add...

Starting with iOS 14, we can write apps that are fully built using SwiftUI, dropping the need to have AppDelegate and SceneDelegate files entirely. For as long as I remember, I've handled deeplinks in my AppDelegate and for the past year in the SceneDelegate. So when Apple introduced developers to this new @main annotated App struct style of building apps, I'm sure we all had the same question on our mind. How does the new App struct work with deeplinks and other tasks that are normally performed in the AppDelegate? Luckily, Apple engineers made sure that handling deeplinks in our...

Tons of apps that we build feature lists. Sometimes we build lists of settings, lists of todo items, lists of our favorite pictures, lists of tweets, and many other things. Some of these lists could scroll almost endlessly. Think of a Twitter timeline, a Facebook feed or a list of posts on Reddit. You might argue that knowing how to build a list that scrolls infinitely and fetches new content whenever a user reaches the end of the list is an essential skill of any iOS developer. That's why as one of my first posts that covers SwiftUI I wanted...

Apple introduced SF Symbols in iOS 13. SF Symbols allow developers to easily integrate icons in their apps. The SF Symbols icons integrate really well with the default system font, and provide a consistent look throughout the system. In iOS 14, Apple added over 750 new icons to the SF Symbols library for developers to use in their apps. Additionally, Apple has expanded SF Symbols to include multi-colored icons. For a full overview of the available SF Symbols that are available, including the newly added and multicolor symbols, download the SF Symbols 2 app from Apple's SF Symbols page. To...

In WWDC2020's session Lists in UICollectionView a slide is shown where a UICollectionViewListCell's separator inset is updated by assigning a new leading anchor to separatorLayoutGuide.leadingAnchor. Unfortunately, this doesn't work in when you try to do it. To set the separator inset for a UICollectionViewListCell you can update the leading anchor constraint by overriding updateConstraints in a UICollectionViewListCell subclass. Setting the anchor in init will cause the system to override your custom anchor leaving you with the default inset. override func updateConstraints() { super.updateConstraints() separatorLayoutGuide.leadingAnchor.constraint(equalTo: someOtherView.leadingAnchor, constant: 10).isActive = true } You can set the leadingAnchor constraint just like you would...