Скачать или смотреть How to Delegate a Call to a Method in json_serialization for Flutter and Dart

Learn how to properly implement `json_serialization` in your Dart code to ensure nested objects serialize as expected, including demonstrating how to delegate calls between classes effectively.
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How to Delegate a Call to a Method in json_serialization

In the world of Flutter and Dart programming, one of the most common tasks developers face is properly managing data formats, specifically with JSON serialization. You may have encountered a situation where you want to serialize nested objects efficiently. This guide will unveil the solution to a common problem when using the json_serializable package: how to ensure that nested class instances are serialized correctly.

The Problem

Let's say you have two classes: Foo and Bar. Your Foo class contains an instance of Bar. Here’s the initial code that you might implement:

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

When you serialize an instance of Foo, you may expect it to print something like { bar: "hi" }, but instead, you encounter the output:

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

The issue is that the nested Bar instance is not being serialized correctly.

The Solution: Using explicitToJson

To resolve this issue, you can utilize the explicitToJson parameter provided by the json_serializable package. By enabling this option, you instruct the serializer to call the toJson method of the nested class (Bar) whenever it encounters an instance of it within the parent class (Foo).

Here’s how you do it:

Modify the Foo class:

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

Explanation:

By adding explicitToJson: true to the @ JsonSerializable() annotation of the Foo class, you are telling the serializer to use the toJson method defined in any nested classes.

Example of Serialization:
After making this adjustment, you can create and serialize an instance of Foo as follows:

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

Expected Output:

Now, when you run your code, the output will be:

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

Conclusion

By utilizing the explicitToJson option in your @ JsonSerializable() annotation for classes containing nested objects, you can effectively manage the serialization of complex data structures in Dart and Flutter. This helps maintain clean and efficient code without needing to override default methods, ensuring that your data is serialized correctly in JSON format.

With these adjustments, you're now equipped to handle JSON serialization in Flutter with ease!



This approach not only clarifies how to resolve the specific problem but enhances the overall utilization of the json_serializable library, making your development process smoother and more efficient.