Getting event via reflection

Question

Iam trying to get the Click event of a button via reflection and this is my code :

Assembly assem = Assembly.GetExecutingAssembly();

Type tExForm = btnSave.GetType();
Object exFormAsObj = Activator.CreateInstance(tExForm);

EventInfo evClick = tExForm.GetEvent("Click");
Type tDelegate = evClick.EventHandlerType;

MethodInfo miHandler=
btnSave.GetType().GetMethod("Click",
BindingFlags.NonPublic | BindingFlags.Instance);

Delegate d = Delegate.CreateDelegate(tDelegate, btnSave, miHandler);

MethodInfo addHandler = evClick.GetAddMethod();
Object[] addHandlerArgs = { d };
addHandler.Invoke(exFormAsObj, addHandlerArgs);

However the miHandler variable is always null!

Note The main issue I am concerned in is how to invoke an event of a specific control at run time, is there a way? For example I want to choose which click event to trigger when the user presses F1.

sorry , typing issue I corrected the code , the miHandler is of type MethodInfo — Hasan Shouman, May 09 '14 at 15:12
You are trying to get a Click event. There is no method named `Click` on a button, why are you calling `GetMethod`? — Yuval Itzchakov, May 09 '14 at 15:17
So... are you trying to actually *raise* the Click event via reflection? — Rex M, May 09 '14 at 15:33

Rex M · Answer 1 · 2014-05-09T19:06:40.717

Based on additional comments below the question, the real goal is to raise an event via reflection.

I'll start by saying this is almost guaranteed to be a really terrible idea. It's going to be error-prone and brittle; it's just asking for bugs. What I'd recommend instead is having many event handlers (button click handler, keypress event handler, etc.) all simply call a common method which does the actual thing you want.

That having been said, here's how to do it. Reflection is always brittle, and this is a prime example of it - you have to rely on the current implementation details of how events in .NET work, which could change tomorrow, and this will stop working. You get a private field stored on the object which holds references to all the subscribing event handlers, loop through each one and invoke it. You also need to manually create the arguments that will be passed (like the EventArgs):

var eventArgs = EventArgs.Empty; //replace with real args

var eventInfo = tExForm.GetType().GetEvent("Click", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
var eventDelegate = (MulticastDelegate)tExForm.GetType().GetField("Click", BindingFlags.Instance | BindingFlags.NonPublic).GetValue(tExForm);
if (eventDelegate != null)
{
  foreach (var handler in eventDelegate.GetInvocationList())
  {
    handler.Method.Invoke(handler.Target, new object[] { tExForm, eventArgs });
  }
}

score 3 · Answer 2 · edited Dec 23 '16 at 17:21

3

You should include the BindingFlag.FlattenHierarchy since Click is defined on Control, not Button.

EventInfo miHandler =
  btnSave.GetType(). GetEvent("Click",
  BindingFlags.FlattenHierarchy | BindingFlags.Instance);

edited Dec 23 '16 at 17:21

djv

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answered May 09 '14 at 15:15

Patrick Hofman

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`Click` isn't a method, so `GetMethod()` is still going to return null. – Rex M May 09 '14 at 15:18
@RexM: so simple and I overlooked. Updated. – Patrick Hofman May 09 '14 at 15:19
I'm not sure this is going to fix OP's problem, though. – Rex M May 09 '14 at 15:20
Got no compiler here so I am not entirely sure, but I think miHandler shouldn't be null any more now. – Patrick Hofman May 09 '14 at 15:21
1

As I understand the problem, OP is not having any trouble getting the EventInfo for Click, s/he's having trouble getting the MethodInfo for the event delegate. – Rex M May 09 '14 at 15:23
@PatrickHofman I tried BindingFlag.FlattenHierarchy , but didn't work ! – Hasan Shouman May 09 '14 at 18:10

Getting event via reflection

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