Effective Data Communication Between Two ObservableObjects in SwiftUI

Learn how to facilitate seamless data communication between two independent `ObservableObject`s in SwiftUI using Combine effectively.
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Unlocking Data Communication Between Two ObservableObjects in SwiftUI

When building SwiftUI applications, you may encounter scenarios where multiple ObservableObjects need to communicate with each other. Suppose you have two independent ObservableObjects — ViewModel1 and ViewModel2 — and you want ViewModel1 to react to changes in an array of strings managed by ViewModel2. In this guide, we will explore how to achieve this using Combine and explain the recommended approach in detail.

The Problem Scenario

In our example, ViewModel2 is designed to maintain an array of strings which is defined with the @ Published property wrapper. This means that any changes to this array are tracked by SwiftUI. However, we want ViewModel1 to be informed every time there is a modification to this array in ViewModel2. So, the question arises — what's the best way to facilitate this data communication effectively?

Recommended Solution: Using Combine

Luckily, Swift's Combine framework offers us a powerful solution for this, simplifying the process of subscribing to changes in one observable object from another. Let's break down the implementation step-by-step.

1. Setting Up Your ViewModels

We will define our two ObservableObjects (ViewModel1 and ViewModel2) as follows:

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2. Creating the Main View

Next, we will create our main ContentView, which links both view models together using the Combine framework:

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3. The Child View

We also create a child view (ChildView) that allows for re-connecting to a different instance of ViewModel2:

[[See Video to Reveal this Text or Code Snippet]]

4. Testing the Implementation

To test the functionality, you can perform the following actions:

Press the "add item" button in the ContentView; this action will append a new string to ViewModel2, and you will see ViewModel1 receiving and printing the updated strings in the console.

Then, press the "Connect child publisher" button in the ChildView; this action alters the connection and will notify ViewModel1 of changes from the child view's instance of ViewModel2.

5. Understanding the Mechanism

For this communication strategy to work efficiently, you must maintain a reference to both ViewModel1 and ViewModel2. This can be easily achieved through dependency injection or using an EnvironmentObject. Instead of a single subscriber, ViewModel1 can be modified to handle multiple connections by changing the cancellable to a Set<AnyCancellable>.

Additionally, leveraging AnyPublisher decouples the implementations, which means you can connect other view models, like ViewModel4, to ViewModel1 seamlessly.

Conclusion

In summary, using Combine to facilitate data communication between two ObservableObjects can greatly enhance the responsiveness of your SwiftUI applications. By following the steps outlined above, you can ensure that your view models stay in sync, resulting in a more dynamic and interactive user experience. So go ahead, implement this approach, and watch your SwiftUI apps come to life!