Скачать или смотреть How to Encode Objects to JSON in Flutter

Learn how to easily convert your Flutter objects into JSON format, ensuring your API requests send data correctly.
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This video is based on the question https://stackoverflow.com/q/65734213/ asked by the user 'Umesh Chakradhar' ( https://stackoverflow.com/u/7741106/ ) and on the answer https://stackoverflow.com/a/65734296/ provided by the user 'Pavneet_Singh' ( https://stackoverflow.com/u/4936904/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Encode Objects to JSON in Flutter: A Step-by-Step Guide

When developing mobile applications using Flutter, sending data to a server often involves converting your objects into JSON format. This is essential for properly structuring your POST requests. In this guide, we'll walk through a common problem with encoding objects to JSON in Flutter, along with a clear solution.

The Problem: Sending a Student Object

Consider a scenario where you have a Student object that contains details about a student, including a nested Subject object that contains information about the subject they are studying. Here is a basic structure of both classes:

Subject Class

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Student Class

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The Issue

When you attempt to encode the Student object to JSON using the following line of code, you encounter a problem:

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You find that the Subject value is null. The reason for this issue lies in the way you are calling the toJson() method of the Subject object.

The Solution: Await the Future Properly

To successfully encode the Subject object within the Student object, you need to ensure that you properly await the result of the toJson() method in the Student class. Here’s how you can do it:

Corrected Student Class Method

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Why This Works

Using await is crucial here because:

Completing the Future: By adding await before sub.toJson(), you allow the asynchronous function to complete and return the desired JSON map.

Preventing Null Values: Without await, the method returns a future object immediately, which could lead to null values when the data is accessed at a later time.

Final Steps: Sending the Data

Once you've made these changes, you should be able to encode your Student object without issues:

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Now, data will correctly include all fields from both Student and the nested Subject object, ensuring that your API request is formatted correctly.

Conclusion

Encoding objects to JSON in Flutter may seem daunting at first, especially with nested objects. However, by ensuring that you correctly await all required futures in your toJson() methods, you can streamline your data preparation for API interactions.

Feel free to reach out if you encounter further issues or have additional questions about Flutter and JSON handling!