Learn more about Combine

A common use of a Core Data store is to cache data from a remote resource locally to support offline functionality of an app. There are multiple ways to implement a caching mechanism and many of them don’t involve Core Data. For example, you could simply fetch a JSON file from a server and store […]

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 […]

In SwiftUI, views can be driven by an @Published property that’s part of an ObservableObject. If you’ve used SwiftUI and @Published before, following code should look somewhat familiar to you: class DataSource: ObservableObject { @Published var names = [String]() } struct NamesList: View { @ObservedObject var dataSource: DataSource var body: some View { List(dataSource.names, id: […]

If you have a Combine publisher and you want to ignore the first n elements that are published by that publisher, you can use the dropFirst(_:) operator. This operator will swallow any values emitted until the threshold you specify is reached. For example, dropFirst(1) will ignore the first emitted value from a publisher: [1, 2, […]

Last week, my attention was caught by a question that Dennis Parussini asked on Twitter. Dennis wanted to recursively make calls to a paginated API to load all pages of data before rendering UI. Since I love Combine and interesting problems I immediately started thinking about ways to achieve this using a nice, clean API. […]

There are several ways to handle errors in Combine. Most commonly you will either use catch or replaceError if you want to implement a mechanism that allows you to recover from an error. For example, catch is useful if you want to retry a network operation with a delay. The catch and replaceError operators look […]

Combine comes with a handy retry operator that allows developers to retry an operation that failed. This is most typically used to retry a failed network request. As soon as the network request fails, the retry operator will resubscribe to the DataTaskPublisher, kicking off a new request hoping that the request will succeed this time. […]

A question that often comes up when folks get into learning Combine is “how do I test code that uses Combine?”. In this week’s post, I will briefly explain the basics of testing Combine code. I will assume that you already know the basics of testing and Combine. If you’re just getting started with both […]

One of Combine’s somewhat painful to work with features is its error mechanism. In Combine, publishers have an Output type and a Failure type. The Output represents the values that a publisher can emit, the Failure represents the errors that a publisher can emit. This is really convenient because you know exactly what to expect […]

When we write code, we write bugs. It’s one of the laws of the universe that we can’t seem to escape. The tools we have to discover, analyze and fix these bugs are extremely important because without good debugging tools we’d be poking at a black box until we kind of figure out what might […]