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A guide on how to handle server error messages in SwiftUI, specifically how to decode and present error messages from API responses in your app.
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How to Display Error Messages from Server in SwiftUI URLSession

When building a SwiftUI app, one essential task involves handling user inputs effectively—especially when integrating with an API for functionalities like user registration. You may encounter situations where an API response indicates an error, such as a conflict with a username or email address that already exists. This guide will guide you through how to display specific error messages from your server using SwiftUI while ensuring a seamless user experience.

The Problem Statement

Imagine a user trying to create an account by filling out a signup form. The details entered might include a username and an email address. If these credentials are already in use, your API responds with an error message (usually a 422 HTTP status code) indicating the failure, but the user sees nothing specific—only a generic message. This raises two crucial issues:

How do you capture and display these specific error messages from the server in SwiftUI?

Is there a way to pre-validate these credentials (like checking if the username or email exists) before the signup process is triggered?

Let's unpack both of these concerns by breaking down the solution into manageable sections.

Understanding the Error Response Structure

The API you’re working with returns a JSON structure when an error occurs during a signup attempt. Here's an example:

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

From this output, the most important pieces of information are available in the errors field, which tells you exactly what went wrong. To properly handle this response in your Swift app, we need mechanisms to decode both normal and error responses effectively.

Implementing Error Handling in Your Service

Step 1: Create an Error Response Struct

You’ll want to create a specific struct to handle any errors returned from your API. This ErrorResponse struct will look something like this:

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

Step 2: Modify the Existing Logic for Parsing Responses

In your SignUpService class, you will decode either a LoginResponse (for successful signups) or the ErrorResponse (for failed attempts). Here's an updated version of your signUp method:

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

This updated logic ensures that you can differentiate between a successful signup and any errors that arise, providing useful feedback to the user.

Step 3: Pre-Validation of Credentials

Finally, to implement the pre-validation of usernames and emails, you should create an API endpoint in your Rails application that checks for existing users before trying to create a new account. This could be a simple GET request that returns a success message if the username or email is available. Here’s a general approach:

Create a New API Endpoint: Set it up to check username/email availability.

Call This Endpoint on Input Change: Use Swift's onChange modifier to call this endpoint whenever the user types into the username or email field.

This pre-validation gives users immediate feedback instead of waiting for an unsuccessful signup.

Conclusion

Handling error messages appropriately can significantly improve user experience in your SwiftUI applications. By implementing a structured approach to decode API responses and providing pre-validation, you can help prevent frustrating signup errors and facilitate smoother interactions. Adapting your services to manage expected errors will allow you to present meaningful messages that guide your users effectively.

Now you're ready to implement these techniques in your app. Happy coding!