Скачать или смотреть Understanding and Fixing the Unhandled Exception Error When Parsing JSON in Flutter

Learn how to resolve the `type 'List dynamic ' is not a subtype of type 'Map String, dynamic '` error in Flutter while parsing a JSON list of objects with proper code examples and explanations.
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This video is based on the question https://stackoverflow.com/q/62909257/ asked by the user 'Ayren King' ( https://stackoverflow.com/u/13430888/ ) and on the answer https://stackoverflow.com/a/62909499/ provided by the user 'julemand101' ( https://stackoverflow.com/u/1953515/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding and Fixing the Unhandled Exception Error When Parsing JSON in Flutter

When working on Flutter applications, you might encounter Unhandled Exception errors when trying to parse JSON data. A common scenario is when you're attempting to deserialize a JSON list into Dart objects. If you've run into the error message:

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

you’re not alone. This guide will guide you through understanding what this error means and how to effectively solve it.

The Problem: What Causes the Error?

This error typically occurs due to a mismatch between the data structure of your JSON response and the expected type in your Dart code. In your specific case, you are working with a JSON file that represents a list of player objects, but the code is trying to treat this list as a single map.

Key Issues in Your Code

Wrong Data Type: The response you receive from your JSON file is a list, but your model's fromJson factory method expects a map. This is the root of the type error.

Incorrect JSON Structure: Your current implementation assumes there's a key named players in the JSON that contains the player data, but this isn't true for your provided JSON structure.

The Solution: How to Fix the Error

To resolve the issue effectively, you need to modify your data parsing logic to correctly handle the JSON list. Below is a step-by-step breakdown of how to adjust your code.

Step 1: Define Your Player Model

To deserialize the player objects, we first need to ensure that you have a proper model class that accepts the correct structure. Here’s an updated version of the Player class to reflect the existing JSON structure:

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

Step 2: Modify the Data Loading Logic

Next, we need to appropriately load the player list from the JSON file. Make sure your loading and parsing method looks like this:

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

Step 3: Call the Updated Logic

Finally, in your home page setup method, ensure you’re using the updated function that returns a list of players:

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

Conclusion

By following the steps outlined above, you should be able to successfully parse your JSON data without encountering any type errors. Remember that understanding the structure of your JSON data is key to appropriately mapping it to your Dart model classes. With these adjustments, your Flutter application should run smoothly without throwing the Unhandled Exception. Happy coding!