Скачать или смотреть Fixing the type 'String' is not a subtype of type 'Map String, dynamic ' Error in Flutter API Calls

Learn how to resolve the common `type 'String' is not a subtype of type 'Map String, dynamic '` error in your Flutter application when calling APIs. Follow the steps for debugging and fixing your model to ensure seamless data processing.
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This video is based on the question https://stackoverflow.com/q/73414918/ asked by the user 'Mıktad Tahir Durak' ( https://stackoverflow.com/u/15728644/ ) and on the answer https://stackoverflow.com/a/73415043/ provided by the user 'Ivo' ( https://stackoverflow.com/u/1514861/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Error: type 'String' is not a subtype of type 'Map<String, dynamic>'

If you're developing a Flutter application and you're making API calls, you may have encountered the error message:

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

This error typically arises when the data returned from an API is not in the expected format. It can be frustrating, especially if you are new to Flutter or API interactions. But don't worry! In this guide, we will break down this error and guide you through the solution step by step.

What Causes This Error?

This error usually occurs when your application expects to receive a valid JSON object, but instead, it receives a string—often an empty string or an unexpected value. In your Flutter code, when you attempt to parse this string as a map (which it is not), the error will surface.

Common Causes

Incorrect API URL: The endpoint you are reaching out to might not be correct or might not return a JSON response as expected.

Mismatched Data Structures: The model defined for JSON parsing does not match the structure of the actual response.

Solution: Updating Your API Call and Model

Here are the steps to rectify the error. Follow along to ensure your API calls work correctly with the expected JSON data format.

Step 1: Check the API URL

First, verify your API endpoint. In your case, the current URL is:

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

Make sure this URL provides a valid JSON response that matches your model structure. You might want to test it separately in a browser or a tool like Postman to inspect the returned data.

Step 2: Update the JSON Parsing Logic

In your model, particularly in the EconomylistXml.fromJson method, locate the following line:

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

This line attempts to parse the JSON object located at json["rss"]. However, using an empty string as a fallback leads to the error. Instead, change the line to:

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

By doing so, you provide an empty map as a fallback instead of a string, which allows the parsing function to receive the correct type.

Step 3: Verify the Model’s Structure

Ensure that your data model (EconomylistXml, Rss, Channel, etc.) accurately represents the expected structure of the JSON response. If the actual JSON response contains different fields or types, you will need to adjust your Dart models accordingly. For example, checking if there are any optional fields you might need to handle correctly.

Step 4: Test the Changes

After making these updates, run your application again. Monitor the console closely for any additional error messages or warnings. If you implemented the aforementioned changes correctly, the error should no longer appear, and you should be able to retrieve and display your data as intended.

Conclusion

In summary, the type 'String' is not a subtype of type 'Map<String, dynamic>' error occurs typically due to mismatched types when parsing JSON data. By ensuring the API URL is correct, adjusting your error handling with a fallback to an empty map, and validating your data structure, you can effectively resolve this issue.

With these adjustments in mind, you should be equipped to handle similar errors in the future with confidence. Happy coding!