Solving the Issue: List dynamic is Not a Subtype of Map String, dynamic in Flutter JSON Parsing

A comprehensive guide to understand and solve the Flutter error that states: `List dynamic ` is not a subtype of `Map String, dynamic `, especially when working with JSON data.
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Understanding and Solving the JSON Parsing Issue in Flutter

If you're diving into Flutter and working with JSON data, you may have stumbled upon a common error: List<dynamic> is not a subtype of Map<String, dynamic>. This error typically arises when you attempt to parse JSON data into a model that expects a different format. In this blog, we'll explore the origins of this error, why it occurs and provide a step-by-step solution.

The Problem

Here's the relevant excerpt of the problematic code:

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

Error Message Breakdown

The Flutter error message states:

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

This indicates that the JSON file you are trying to decode is an array (or a list) of book objects, not a single object, leading to the type mismatch with your fromJson method.

The Solution

To correctly parse the list of book objects from your JSON, you need to take the following steps:

Step 1: Change the getBooksAll() Method

Instead of expecting a Map<String, dynamic> in your fromJson method, you should modify the getBooksAll() method to handle a list of objects. Here’s how you can do it:

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

Step 2: Adjust the Id Handling

In your original code, you were using a separate Id class to handle the ID parsing. However, since the ID is of type integer rather than a complex object, it's better to directly use int? in your BookData class. Thus, simply adjust the related parts like this:

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

Final Step: Using the Updated Function

Now that your getBooksAll method correctly parses the JSON data, you can fetch and use a list of book objects like this:

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

Conclusion

Understanding the root cause of Flutter’s JSON parsing error can save you a lot of headaches as you develop your applications. By adapting your parsing method to handle lists instead of single objects, you can easily fix the incompatibility issues. Keep these adjustments in mind as you work with JSON data in Flutter, and you'll find that you can efficiently manage and display data in your apps.

Happy coding!