Скачать или смотреть Solving the type 'List dynamic ' is not a subtype of type 'String' Error in Flutter

Learn how to fix the common `type 'List dynamic ' is not a subtype of type 'String'` error when fetching data from APIs in Flutter. Follow our step-by-step guide for a seamless development experience.
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Understanding and Resolving the type 'List<dynamic>' is not a subtype of type 'String' Error in Flutter

When working with Flutter, especially when fetching data from APIs, developers often encounter various errors. One such error is the infamous type 'List<dynamic>' is not a subtype of type 'String'. This issue commonly arises when the expected data structure in your code does not match the actual data format returned by the API. In this guide, we will explore this error in detail and how you can successfully fix it.

The Background of the Problem

You may have followed the Flutter documentation to fetch data from a mock API using the HTTP package. However, sometimes the structure of the data you are trying to work with can seem confusing. Let's take a look at the specific issue you might be facing. You have defined your Groceries model to include the following fields:

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

When you call your fetchGroceries function, it seems to expect a single Groceries object, but the API returns a list of grocery items, which is where the error occurs. You are effectively trying to assign a List<dynamic> to a Groceries type, causing the error message.

How to Fix the Error

Step 1: Modify the Fetching Function

To handle the list of grocery items returned by the API, you will need to adjust the fetchGroceries function to return a Future<List<Groceries>>. You'll change your code as follows:

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

Step 2: Update Your FutureBuilder

Next, you will need to update your FutureBuilder to accommodate the list of grocery items returned from the modified function. Here's the revised snippet:

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

Step 3: Verifying the Data Structure

Lastly, verify that the API response is in the correct format as you expect in your application. The expected response should look like this:

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

Ensure that when you decode this JSON data, the field names (name, id, images) fit perfectly with your Groceries class.

Conclusion

By adjusting your fetching code to accommodate a list of items and modifying the FutureBuilder to iterate through the list correctly, you can resolve the type 'List<dynamic>' is not a subtype of type 'String' error. This process not only clarifies the structure of the data being manipulated but improves overall data handling within your Flutter application.

By following these steps, you can have a seamless API connection and effectively display the retrieved data in your Flutter app. Happy coding!