Resolving the Error: Flutter 'List dynamic ' is not a subtype of type 'Map String, dynamic '

Learn how to resolve the common issue in Flutter where a List is mistaken for a Map, ensuring smooth data handling from API responses.
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Resolving the Error: Flutter 'List<dynamic>' is not a subtype of type 'Map<String, dynamic>'

When working with Flutter applications, it’s common to encounter various errors during runtime, especially when dealing with data from APIs. One such issue that many developers face is the error that states, List<dynamic>' is not a subtype of type 'Map<String, dynamic>'. This can be confusing, especially for beginners, but understanding how to address it is crucial for building robust applications.

Understanding the Problem

This particular error indicates that the structure of the data you're trying to decode does not match what your app expects it to be. In Flutter, this often arises when you are trying to decode JSON data, and you've mistakenly assumed the data type of the response.

In your specific case, when you called an API, the response returned a List of objects rather than a Map. This mismatch is what triggers the error.

JSON Structure

The JSON response you're handling looks like this:

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

As you can see, this is an array (or a list) of objects, each representing a story with its respective properties.

The Solution

To fix the issue and properly handle the data structure returned by your API, you will need to modify the type of your variable that holds the decoded data.

Step 1: Change the Type Declaration

Instead of declaring _map as a Map<String, dynamic>, you should declare it as a List<Map<String, dynamic>>:

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

Step 2: Update the JSON Decoding

Next, you’ll need to ensure that you convert the JSON response to a list of maps correctly. Here's how you can do that:

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

Complete Code Example

With these modifications, your fetchdata function should look something like this:

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

Result

With these changes, your application should now correctly handle the JSON data, without running into type-related issues. The error message indicating that a List<dynamic> is not a subtype of a Map<String, dynamic> should no longer appear. Instead, your Flutter app will be able to decode and display the API data effectively, allowing users to interact with the content seamlessly.

Conclusion

In conclusion, errors related to type mismatches can be a common hurdle when developing with Flutter, especially when dealing with dynamic data types from APIs. By ensuring that your data types accurately reflect the structure of the incoming JSON, you can avoid these pitfalls and enhance the stability of your application. Happy coding!