Get delegate handler from event

Question

I am trying to get the event handler without doing any changes in MyControl class. I tried to use reflection but I am not able to get the handler. Following is a code sample. Thanks

public class MyControl : Control
{
    public void Register()
    {
        SizeChanged += MyControl_SizeChanged;
    }

    void MyControl_SizeChanged(object sender, EventArgs e)
    {
        // Do something
    }
}

//[TestFixture]
public class MyControlTest
{
    //  [Test]
    public void RegisterTest()
    {

        var control = new MyControl();
        control.Register();

        var eventInfo = control.GetType().GetEvent("SizeChanged", BindingFlags.Public | BindingFlags.Instance);

        // Need to get the handler (delegate) and GetInvocationList().Count
        EventHandler handler = ...;

        var count = handler.GetInvocationList().Count();
        Assert.That(count, IsolationLevel.EqualTo(1));
    }
}

The secret cookie name is "EventResize". – Hans Passant Aug 12 '15 at 15:19 — Hans Passant, Aug 12 '15 at 15:19

score 1 · Accepted Answer · answered Aug 12 '15 at 15:14

1

Events don't actually have handlers; an event is just a pair of specially-named add & remove methods.
For more information, see my blog.

How the event stores its handlers is an implementation detail; WinForms controls use an EventHandlerList.
You can see this in the source.

answered Aug 12 '15 at 15:14

SLaks

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But how it helps me to get to the GetInvocationList() method if I do not have the handler? Or let say, how can I use reflection to get the EventHandler?\ – ehh Aug 12 '15 at 15:23
@ehh: You can use lots of reflection to get the protected HandlerList and the private key object. However, you probably shouldn't be doing this. – SLaks Aug 12 '15 at 15:25
so how can I achieve this test, I need to ensure that Register method is covered by RegisterTest unit test. – ehh Aug 12 '15 at 15:28

score 0 · Answer 2 · answered Aug 12 '15 at 15:13

0

That's probably because of it's protection level which is currently private as can be seen from your posted code

void MyControl_SizeChanged(object sender, EventArgs e)
{
    // Do something
}

answered Aug 12 '15 at 15:13

Rahul

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That's not what he's trying to do. – SLaks Aug 12 '15 at 15:15

Get delegate handler from event

2 Answers2