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Learn how to leverage Dart's reflection API to dynamically invoke methods and obtain their results with ease.
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How to Use Dart's Reflection API to Retrieve Results from Invoked Methods doWork

Dart offers a powerful feature called reflection, which enables developers to inspect and modify the structure of their programs at runtime. This capability can be incredibly useful, particularly when you want to dynamically invoke functions and retrieve their results. In this guide, we’ll tackle a common challenge: How can you obtain the result returned by a method invoked using Dart's reflection API? Let’s break it down step-by-step.

Understanding the Problem

Imagine you have a simple service class that executes a task and returns some data. You are using Dart's mirror API to invoke this method dynamically but struggle to get the returned result. Here is the relevant code snippet illustrating the setup:

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The Issue

You see the output "doing work", confirming that the method is invoked, but retrieving the actual result remains elusive. The challenge lies in understanding how to access the result stored within the InstanceMirror. Let’s explore how to achieve this.

Step-by-Step Solution

1. Import Necessary Libraries

First, ensure you import the dart:mirrors library, as it's essential for working with reflection in Dart:

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2. Define Your Classes

Next, we define our classes, as shown in the original code:

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3. Reflect and Invoke the Method

In the main() function, create an instance of MyService and obtain its mirror representation:

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4. Access the Result

The key to obtaining the result from the method lies in the reflectee property of the InstanceMirror. Here’s what the final code looks like with the result extraction:

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5. Explanation of the Code

reflect(instance): This function retrieves the mirror of the MyService instance.

invoke(-doWork, <dynamic>[]): Calls the doWork method dynamically. The - symbol denotes a symbol reference to that method.

result.reflectee: This retrieves the value returned by the doWork method. Note that, since the method returns a Future, you must await this result before accessing its properties.

await (result.reflectee as Future<MyData>): Here, we convert the reflectee to a Future<MyData> and await its completion to access the someString property.

Conclusion

Using Dart’s reflection API, you can dynamically invoke methods and efficiently retrieve their results. Whether you're building applications that require flexibility or need to execute methods based on runtime decisions, reflection is a crucial feature to master. By following the steps above, you can easily access generated results, paving the way for more dynamic and adaptable code.

We hope this guide helps you successfully utilize reflection in Dart. Happy coding!