How to check which event are assigned?

Question

My code is as follows.

Control[] FoundControls = null;
FoundControls = MyFunctionToFilter(TF, c => c.Name != null && c.Name.StartsWith("grid"));
var eventinfo = FoundControls[0].GetType().GetEvents();

However, eventinfo gives me the list of all the controls which belongs to the grid. Whereas there are only two events that are defined that is KeyDown and Validating in the main class.

How can I get a list of these assigned events, that is, Keydown and Validating?

@Jacob Yes.... Because these are the only two events declared in the main class — Rohit, Mar 26 '13 at 06:55
do you mean "event handlers declared" instead of "two events declared"? — Julien, Mar 26 '13 at 07:02
yes it is winform..and in my main form i have private void gridControl1_EditorKeyDown(object sender, KeyEventArgs e) { } — Rohit, Mar 26 '13 at 07:04
@Kyle one more question - you need to get assigned events of DataGridView only, or for any control? — Sergey Berezovskiy, Mar 26 '13 at 07:27
Explain your real problem. Why would you want to know the available events? Why not just subscribe to the events you're interested in? This is like calling the bus company whether their buses have Diesel engines in them, while you actually just want to get from A to B. — CodeCaster, Mar 26 '13 at 07:30
Essential follow-ups: Why are you doing this ? What are you trying to achieve ? There may be something out there which solves your need as-is. — Alex, Mar 26 '13 at 07:59

score 5 · Accepted Answer · edited Sep 09 '13 at 16:21

Windows Forms (WinForms) has a tricky model of events for components (and DataGridView is a component). Some events are inherited from Control (like FontChanged, ForeColorChanged, etc.), but all specific to component events are stored in a single EventHandlerList object, which is inherited from Component (BTW, events from Control are also stored there, see the update at the end of the answer). There is a protected Events property for that:

protected EventHandlerList Events
{
    get
    {
        if (this.events == null)            
            this.events = new EventHandlerList(this);            
        return this.events;
    }
}

And here is the way how event handlers are added for DataGridView events:

public event DataGridViewCellEventHandler CellValueChanged
{
    add { Events.AddHandler(EVENT_DATAGRIDVIEWCELLVALUECHANGED, value); }
    remove { Events.RemoveHandler(EVENT_DATAGRIDVIEWCELLVALUECHANGED, value); }
}

As you can see, delegate (value) is passed to EventHandlerList with some key value. All event handlers are stored there by key. You can think about EventHandlerList as a dictionary with objects as keys, and delegates as values. So, here is how you can get components' events with reflection. The first step is getting those keys. As you already noticed, they are named as EVENT_XXX:

private static readonly object EVENT_DATAGRIDVIEWCELLVALUECHANGED;
private static readonly object EVENT_DATAGRIDVIEWCELLMOUSEUP;
// etc.

So here we go:

var keys = typeof(DataGridView) // You can use `GetType()` of component object.
   .GetFields(BindingFlags.NonPublic | BindingFlags.Static | BindingFlags.FlattenHierarchy)
   .Where(f => f.Name.StartsWith("EVENT_"));

Next, we need our EventHandlerList:

var events = typeof(DataGridView) // or GetType()
          .GetProperty("Events", BindingFlags.Instance | BindingFlags.NonPublic);
// Could be null, check that
EventHandlerList handlers = events.GetValue(grid) as EventHandlerList;

And the last step, getting the list of keys, which have handlers attached:

var result = keys.Where(f => handlers[f.GetValue(null)] != null)
                 .ToList();

That will give you the keys. If you need delegates, then simply look in the handlers list for them.

UPDATE: Events which inherited from Control are also stored in EventHandlerList, but for some unknown reason their keys have different names, like EventForeColor. You can use the same approach as above to get those keys and check if handlers are attached.

score 2 · Answer 2 · edited May 23 '17 at 11:48

2

According to the comments in this question showing that this is a Windows Forms related question it's almost not possible to determine assigned event handlers by iterating the list, not without reflection anyway.

The following text is from Hans Passant's answer on a similar question:

Windows Forms has strong counter-measures against doing this. Most controls store the event handler reference in a list that requires a secret 'cookie'. The cookie value is dynamically created, you cannot guess it up front. Reflection is a backdoor, you have to know the cookie variable name. The one for the Control.Click event is named "EventClick" for example, you can see this in the Reference Source or with Reflector.

Knowing the cookie name would help you get the assigned event, but I am not sure if there is such a list with all the names which you could iterate. See this other answer which demonstrates how to get an event from one control where the cookie name is known.

Here you can find another example (which still goes by using a known event name).

edited May 23 '17 at 11:48

Community

1
1

answered Mar 26 '13 at 06:48

CloudyMarble

36,908
70
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1

I don't think it's correct answer. EventInfo always will not be null – Sergey Berezovskiy Mar 26 '13 at 06:51
1

I get a list of all the events as I was getting before – Rohit Mar 26 '13 at 06:56
2

@TwoMore updated answer is also **incorrect**. You can't just get fields, because in winform `EventHandlerList` is used. Why people keep upvoting incorrect answers? – Sergey Berezovskiy Mar 26 '13 at 07:10
1

Is this a winform question? – CloudyMarble Mar 26 '13 at 07:11
1

@TwoMore yes, see comments to question – Sergey Berezovskiy Mar 26 '13 at 07:12
1

@TwoMore In your mentioned example the event "MyEvent" is known beforehand..... Whereas In my case we are trying to find out which are the eventhandlers declared ..here in this case it is (Keydown and validating) but there could be more...so i dont think the solution helps – Rohit Mar 26 '13 at 07:17
1

@Kyle there is other problem, see my previous comments – Sergey Berezovskiy Mar 26 '13 at 07:19

score 0 · Answer 3 · answered Mar 26 '13 at 07:38

Can't you use reflection to look the list of handlers?

Here is a simple console app looking at handlers hooked on the events of a serial port instance:

using System;
using System.IO.Ports;
using System.Reflection;

class Program
{
    static void OnErrorReceived(object sender, SerialErrorReceivedEventArgs e){}

    static void Main(string[] args)
    {
        var serialPort = new SerialPort();

        // Add a handler so we actually get something out.
        serialPort.ErrorReceived += OnErrorReceived;  

        foreach (var eventInfo in serialPort.GetType().GetEvents())
        {
            var field = serialPort.GetType().GetField(eventInfo.Name, BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.GetField);
            if (field != null)
            {
                var backingDelegate = (Delegate)field.GetValue(serialPort);
                if (backingDelegate != null)
                {
                    var subscribedDelegates = backingDelegate.GetInvocationList();

                    foreach (var subscribedDelegate in subscribedDelegates)
                    {
                        Console.WriteLine(subscribedDelegate.Method.Name + " is hooked on " + eventInfo.Name);
                    }
                }          
            }                     
        }
    }
}

jacob aloysious · Answer 4 · 2013-03-26T07:17:30.430

-1

Based on Kyle comment:

@Jacob Yes.... Because these are the only two events declared in the main class – Kyle

Events would contain KeyDown and Validating events only.

        Control a = new TextBox();
        var events = a.GetType().GetEvents().Where(eventInfo => eventInfo != null && (eventInfo.Name == "KeyDown" || eventInfo.Name == "Validating"));

+events.ToList()[0] {System.Windows.Forms.KeyEventHandler KeyDown}

+events.ToList()[1] {System.ComponentModel.CancelEventHandler Validating}

edited Mar 26 '13 at 07:17

answered Mar 26 '13 at 07:08

jacob aloysious

2,547
15
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I didn't donwvote your answer, but it's not correct answer. OP want to define which events have handlers assigned – Sergey Berezovskiy Mar 26 '13 at 07:29
@lazyberezovsky: I understood the issue after seeing this: http://stackoverflow.com/questions/3855985/find-all-event-handlers-for-a-winforms-control-in-net/3856171#3856171 . Thanks! – jacob aloysious Mar 26 '13 at 07:32

How to check which event are assigned?

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