Swift Combine: A Hands-On Guide

Swift Combine is a framework introduced by Apple in 2019 that provides a functional reactive programming solution for Apple platforms. It enables developers to subscribe to values and perform transformations on them, making it easier to handle asynchronous events and complex data flows.

In this article, we will explore the basics of Swift Combine and demonstrate how it can be used in real-world applications with code examples.

First, let’s take a look at the core components of Swift Combine: Publishers, Subscribers, and Operators.

Publishers: Publishers are the sources of values that are emitted over time. They can emit values in response to external events, such as network responses or user inputs, or they can generate values on their own, such as a timer or a sequence of values.
Subscribers: Subscribers are the receivers of values that are emitted by publishers. They can receive values and perform actions based on these values, such as updating a UI or storing data.
Operators: Operators are functions that can be applied to values emitted by publishers. They can be used to filter, map, reduce, or combine values, among other things.

With these core components in mind, let’s take a look at a simple example of how Swift Combine can be used to handle user inputs.

Swift

import Combine

class ViewModel {
  let username = CurrentValueSubject<String, Never>("")
  var isValid: AnyPublisher<Bool, Never> {
    return username
      .map { $0.count >= 3 }
      .eraseToAnyPublisher()
  }
}

let viewModel = ViewModel()

let cancellable = viewModel.isValid
  .sink { value in
    print("username is valid: \(value)")
  }

viewModel.username.send("John")
// Output: "username is valid: true"

viewModel.username.send("Jo")
// Output: "username is valid: false"

In this example, we have a ViewModel class that contains a username property, which is a CurrentValueSubject that emits the current username. We also have a computed property isValid that returns a publisher that emits a Boolean value indicating whether the username is valid (i.e., if it has a length of at least 3 characters).

We create an instance of ViewModel and subscribe to the isValid publisher using the sink operator. This operator receives the emitted values and performs an action, in this case, printing the Boolean value to the console.

Finally, we update the username by sending new values to it, which causes the isValid publisher to emit new values.

This simple example demonstrates how Swift Combine can be used to handle user inputs in a reactive manner. The username property acts as the source of values, the isValid publisher acts as a transformation of these values, and the sink operator acts as the receiver of the transformed values.

In conclusion, Swift Combine provides a powerful and efficient way to handle asynchronous events and complex data flows in Apple platforms. By combining publishers, subscribers, and operators, developers can create reactive and declarative systems that are easier to maintain and understand. Whether you’re working on iOS, macOS, or other Apple platforms, Swift Combine is a valuable tool to have in your arsenal.

Leave a Reply