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Discover effective methods for sending array data in POST requests using Flutter. Avoid common pitfalls related to duplicate keys in form data.
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How to Handle Array Data in POST Form with Flutter

When working with APIs in Flutter, you might encounter situations where you need to send an array of data using POST requests. This can become tricky, particularly when dealing with form data that has duplicate keys. In this post, we'll explore how to properly format and send array data in a POST request using the Flutter HTTP package, drawing from a common scenario in app development.

The Problem

Suppose you've prepared a request in Postman that updates an array of data on your website, and now you're trying to replicate this functionality in your Flutter app. Here’s the code you might be starting with in Postman:

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

The challenge arises when Flutter’s handling of form data leads to the removal of duplicate keys, resulting in only one of the values (Web Developer in this case) being sent to the server. You may find yourself wondering how to ensure both values are retained in the request body.

The Solution

To overcome this issue, you can format your data in a way that avoids key duplication. Here are two effective approaches:

Method 1: Structuring Your Data Manually

Instead of adding values directly as follows:

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

You can construct a map that uniquely indexes these values based on their positions in the array. Here's how to do it:

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In this method:

We create a list of values we want to send.

Using a for loop, we generate a map where each value is assigned a unique key based on its index in the array.

This structure allows Flutter to add multiple fields under the same prefix without overwriting previous entries.

Method 2: Using JSON Instead of Form Data

If possible, consider sending your data as a JSON object instead. This generally simplifies sending nested and array data, and is often much cleaner. Here’s how you could do it:

Change the content type to application/json in your headers.

Create a Map and encode it:

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

Why Use JSON?

Ease of structure: JSON allows you to send complex data structures without the issues posed by key duplication.

Support for complex nested data: When your API expects JSON, you naturally take advantage of its capabilities for sending nested and array data.

Conclusion

When sending array data in a POST request with Flutter, careful structuring is key to avoiding common pitfalls like key duplication. Whether you opt for manually indexing your values in form-data or switching to a JSON-based approach, both methods can help you effectively update your data on the server without losing important fields.

By understanding these techniques, you can ensure that your Flutter applications effectively communicate with backend services, keeping your data consistently updated. Happy coding!