c# Adding a listener to Event with only the method name (text)

Question

I am trying to use Reflection to add a method from a class to an event. Here is my setup.

Have a class with a keyPressDown & keyPressUp method. I also have an Event in this class. keyPressDown & keyPressUp will fire whatever methods are subscribed to it (if any).

These additional methods are controlling RGB light emitting diodes. One method can flash a color, another can fade a color, etc..

I can subscribe to the event like myEventKeyUp += myClass.MethodA;
My problem is, I am storing the configuration the user wants in a database. So the only thing I can think of is storing the Method Name as text and use reflection to add it to the event handler.

Code Example:

Class MyClass

public event delegateKeyDown keyDownEvent;

public event delegateKeyUp keyUpEvent; 

public void KeyUp()
    {
        joystick.SetBtn(false, 1, vJoyButtonID);
        if (keyUpEvent != null) keyUpEvent();
    }

 public void KeyDown()
    {
        joystick.SetBtn(true, 1, vJoyButtonID);

        // IF WE HAVE ANY LISTENERS THEN FIRE THEM
        if (keyDownEvent != null) keyDownEvent();
    }

public void MethodA()
{
    // DO SOMeTHING HERE
}

Main Form

button.keyDownEvent += button.SetRandomColor;

button.keyUpEvent += button.TurnOff;

What I need to do is something like: button.keyUpEvent += MyClass.GetType().GetMethod("MethodA");

I know you can't do what I am trying to do with Reflection, I read that I can use reflection to get hold of the delegate that contains the event handler, and add it through that way but I am unsure (or unclear about this).

score 0 · Accepted Answer · answered Mar 15 '18 at 05:59

In the vein of Jim W's link, here's a working example:

using System;
using System.Reflection;

internal class Program
{
    private static void Main()
    {
        var foo = new Foo();
        var fooType = foo.GetType();
        var eventInfo = fooType.GetEvent("Bar");
        var methodInfo = fooType.GetMethod("OnBar", BindingFlags.Static | BindingFlags.Public);
        eventInfo.AddEventHandler(foo, Delegate.CreateDelegate(eventInfo.EventHandlerType, methodInfo));

        foo.RaiseBar();

        Console.ReadKey();
    }
}

public class Foo
{
    public delegate void BarHandler(object sender, BarEventArgs args);

    public event BarHandler Bar;

    public void RaiseBar()
    {
        Bar(this, new BarEventArgs());
    }

    public static void OnBar(object sender, BarEventArgs args)
    {
        Console.WriteLine(args.Guid);
    }
}

public class BarEventArgs : EventArgs
{
    public Guid Guid => Guid.NewGuid();
}

Thanks for the help ejohnson. This was the main structure that worked, but had to use typeOf() instead of GetType. I'm not exactly sure why that is?? — Jason G, Mar 16 '18 at 03:33

score 0 · Answer 2 · answered Mar 16 '18 at 03:31

Thanks for both of your help. Between the two examples shown I was able to wrap my head around this. I Made a function to handle the event setup as follows:

 private void SetupEventHandlers(RGBButton button,string EventName, string MethodName)
        {
            // THIS SETS UP THE EVENT HANDLER THAT WILL FIRE ANY ADDITION 
            // ACTIONS THE USER COULD WANT WHEN A BUTTON IS PRESSED OR RELEASED.
            var p = button;
            var eventInfo = p.GetType().GetEvent(EventName);
            var methodInfo = typeof(RGBButton).GetMethod(MethodName);

            try
            {
                // TRY TO SUBSCRIBE TO OUR KEYUP OR KEYDOWN EVENT
                Delegate handler = Delegate.CreateDelegate(eventInfo.EventHandlerType, p, methodInfo);
                eventInfo.AddEventHandler(p, handler);
            }
            catch (Exception)
            {
                // MOST LIKELY COULDN'T FIND THE METHOD WE ARE TRYING TO FIRE
                throw new System.InvalidOperationException("Failed to find method: " + MethodName + "', which is registered as an Event Subscriber.");
            }


        }

This allows me to add to an event in my class (a few different events) with any given name (stored in a database) all from one function. the var P = button is a class which defines my RGB Led arcade buttons. That class contains the events that get triggered when the button is pressed.

c# Adding a listener to Event with only the method name (text)

2 Answers2

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