How Can We Create a Generic `FromEvent` Method for Handling Events of Any Type and Parameter List in C#?

General-Purpose FromEvent Method without Specifying Delegate Type

Problem Statement:

Currently, creating a task based on an event requires defining a custom FromEvent method for each event in each class. This can become cumbersome and repetitive. The goal is to develop a general-purpose FromEvent method that can handle any event on any object.

Challenges:

The main challenges encountered are:

• Passing the event as a string (e.g., "OnCompletion") in code raises an error due to the event only being accessible on the left-hand side of the = or -= operators.
• The delegate of the event is unknown at runtime and needs to vary.
• Emitting IL to set the result of the TaskCompletionSource dynamically.

Solution:

A comprehensive solution involves:

1. DynamicMethod Creation: Create a DynamicMethod for each encountered delegate type. This method dynamically calls the SetResult method of a TaskCompletionSourceHolder class, which in turn sets the result of the task.
2. Reflection: Use reflection to retrieve the EventHandlerType property of the event and create a delegate from the emitted DynamicMethod.
3. Substituting the Generic Type: Utilize the TaskFromEvent extension method instead of manually specifying the delegate type (e.g., TaskFromEvent), as shown in the following code:

object[] result = await obj.FromEvent("Event Name");

This method supports events with any return type and parameter list. It eliminates the need for boilerplate code and allows seamless and reusable handling of events from various objects.

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