Скачать или смотреть Resolving the String is not a subtype of type Map String, dynamic Error in Flutter JSON Parsing

Learn how to tackle the common error in Flutter when parsing JSON by converting a String response into a Map, ensuring your app works seamlessly with server data.
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This video is based on the question https://stackoverflow.com/q/75675807/ asked by the user 'lambduh' ( https://stackoverflow.com/u/14459796/ ) and on the answer https://stackoverflow.com/a/75675847/ provided by the user 'Mateus Venâncio' ( https://stackoverflow.com/u/12521312/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Tackling the String is not a subtype of type Map<String, dynamic> Error in Flutter JSON Parsing

Working with JSON data in Flutter can often pose certain challenges, especially when receiving responses from web sources. One common issue developers encounter is the error message: "String is not a subtype of type Map String, dynamic ". This comprehensive guide will help you understand this problem and offer a straightforward solution to parse JSON responses correctly.

The Problem at Hand

When retrieving JSON data from a server, Flutter may throw an error indicating that a String cannot be parsed into a Map. This typically happens due to how the JSON response is processed in your application code. While hardcoded JSON can be parsed without issues, dynamic responses from your server may require additional steps to ensure proper parsing.

Example Scenario

You may have a JSON object structured like this:

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Despite the correct structure, when fetching this data from the server, you might encounter an error in your parsing logic.

Understanding the Solution

The issue arises because the HTTP request returns the response body as a String, while your Neighbors.fromJson method expects a Map<String, dynamic>. To resolve the issue, you need to convert the response String into a Map before processing it.

Step-by-Step Guide

Import Required Libraries:
Ensure you have imported dart:convert. This library provides the necessary tools to convert JSON strings into Dart objects.

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Decode the JSON Response:
Modify the line where you add the parsed data to use jsonDecode(). Instead of directly passing response.body, decode it first.

Change this line:

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To this:

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Example Code Snippet

Here's how your fetching method might look after applying the correction:

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Conclusion

By converting the String response from your server into a Map using jsonDecode(), you'll resolve the "String is not a subtype of type Map String, dynamic " error and ensure your app can effectively process and utilize the fetched data. Adopting this best practice will enhance your application’s robustness when handling dynamic JSON responses.

Feel free to reach out if you have any questions or encounter other issues while coding!