Скачать или смотреть How to Properly Cast a Parsed JSON Response to a Local Variable in Flutter

Learn how to cast a parsed JSON response from a Model to a local variable in Flutter to eliminate common errors with easy-to-follow steps.
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This video is based on the question https://stackoverflow.com/q/75119861/ asked by the user 'coolhack7' ( https://stackoverflow.com/u/8297485/ ) and on the answer https://stackoverflow.com/a/75121982/ provided by the user 'Victor Eronmosele' ( https://stackoverflow.com/u/11039164/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Solving JSON Casting Errors in Flutter

As a Flutter developer, you may encounter various challenges when working with JSON data. One common issue arises when you're trying to cast a parsed response from a Model class into a local variable, especially if you've been working with JSON data and Models generated from online tools. In this post, we will address a specific problem: the error message type 'LoginModel' is not a subtype of type 'Map<String, dynamic>' and how to resolve it.

Understanding the Problem

To provide some context, let's walk through the JSON response you are working with and the relevant code used to parse this JSON into a model class.

The JSON Response

Here’s a sample JSON response that we are dealing with:

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

The Model Class

You have created a LoginModel class, structured to parse the JSON response. However, the error message you receive indicates that there's an inconsistency in how you use the model and local variable types.

Key Issues Identified

Incorrect Casting: Attempting to treat the LoginModel object as a Map<String, dynamic>, which leads to the type error.

Variable Assignment: The assignment of the parsed response is incorrect, as the local variable _loginResponse is initialized as a Map<String, dynamic> rather than a LoginModel.

Solution Steps

To resolve the issues and correctly store the parsed response into a local variable, follow these steps:

Step 1: Change the Assignment

You'll need to change this line in your LoginController class:

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

to:

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

This change indicates that you should first cast value['data'] to the appropriate type before assigning it.

Step 2: Update the Variable Types

To enhance your code structure, you should consider updating your _loginResponse variable in the LoginController to be of type LoginModel instead of Map<String, dynamic>. Here’s how to change it:

Declare _loginResponse as:

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

Modify the loginResponse getter method to return a LoginModel object instead of a Map<String, dynamic>.

Step 3: Properly Parse the JSON Data

When you parse the JSON data, ensure that you cast value['data'] correctly to a Map<String, dynamic> before passing it to the LoginModel.fromJson() method:

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

Updated LoginController Class

After applying the suggestions, here is how your LoginController class should look:

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

Conclusion

By following these steps, you should be able to effectively cast a parsed JSON response from a model into a local variable in Flutter without encountering type-related errors. Remember that ensuring the corresponding types match clarifies your code and reduces the likelihood of errors. Happy coding!