Extension to "safe invoke"

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**Updated to actually make sense, I hope** Ok folks I am trying to tackle something here but it is over my head. Here is the idea I have a class library that raises events that I want to subscribe to from a winform. When the even is raised I want to use an object in the eventargs to update the form without dealing with a ~~cast~~ invoke (I have multiple threads going on) in the form code itself. Ultimately I found some code online that works but i'd like to write and extension method for it and I'm failing.

Original <slightly modified=""> working code:

C#

public delegate void StatusLogUpdated(object sender, StatusLoggerUpdatedEventArgs e);
public event StatusLogUpdated StatusChanged;



public void AddLog(LogItem logItem)
{
//Some internal stuff

StatusLogUpdated handler = StatusChanged;

if (handler != null)
{
   foreach (StatusLogUpdated singleCast in handler.GetInvocationList())
   {
      ISynchronizeInvoke syncInvoke = singleCast.Target as ISynchronizeInvoke;
      if ((syncInvoke != null) && (syncInvoke.InvokeRequired))
      {
          syncInvoke.Invoke(singleCast, new object[] { this, logEA });
      }
      else
      {
           singleCast(this, logEA);
      }
   }
}
}

Flawed Idea Code

C#

public static void SafeInvoke(this Delegate theDelegate, EventArgs e)
{
   Delegate handler = theDelegate;

   if (handler != null)
   {
      foreach (var singleCast in handler.GetInvocationList())
      {
         ISynchronizeInvoke syncInvoke = singleCast.Target as ISynchronizeInvoke;
         if ((syncInvoke != null) && (syncInvoke.InvokeRequired))
         {
            syncInvoke.Invoke(singleCast, new object[] { null, e });
         }
         else
         {
            singleCast(null, e); // compiler gripes with "'singleCast' is a                   
                                 // variable' but is used like a 'method'"
         }
      }
   }
}

I feel like I'm so close here but I can't seem to figure out what to do instead of the singleCast(null,e); Any thoughts are welcome, I am past my knowledge level. I'm not even fully sure of the ramifications of what I'm trying to do. I'm still pretty new to c# (and programming) so if my terms are off I apologize. Thanks in advance.

Posted 21-Jan-12 18:54pm

rleonard55

Updated 22-Jan-12 15:58pm

v7

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Comments

Sergey Alexandrovich Kryukov 22-Jan-12 2:05am

How can you talk about "without dealing with a cast", if you are trying to do a sequence of slowest dynamic cast "is" in a loop?! What is the purpose of this? Normally, the class derived from EventArgs is designed to avoid casts; sometimes, sender needs a cast though. As to the first sample, what is StatusLoggerUpdatedEventArgs? Can singleCast become null? What the declaring class does and why?

The purpose of iteration through InvocationList is not clear. I used to do it, for a special purpose (please see my article "Dynamic Method Dispatcher" if interested), but "I want to use an object in the eventargs to update the form" does not justify it. Normally, the whole list is invoked in one Invoke method. Same thing with invocation from a non-UI thread. Both things are much simpler in implementation.

Are you sure you know what do you wan to achieve? If you "found some code online" it would be good to understand what it does. At least show a link.

--SA

rleonard55 22-Jan-12 3:13am

I appreciate you taking the time to respond but some of it isn’t necessary. I’m certain if you took the time to read it again you would see that I never actually said what you quote me as saying. I am trying to find a way to not need to deal with any invoke logic (I never brought up case) in the form itself but keep it all in the class library. I’m aware there might be unclear or incorrect ideas conveyed here. This is a ‘question’ not an article. As I said I am new and trying to learn, I acknowledge (as I did in the original post) this may be a bad idea and that I don’t fully understand the ramifications of what I am attempting to do. I’m just trying it.

StatusLoggerUpdatedEventArgs is just derived from generic EvengArgs so that I could attach my own class inside of it. “Can singleCast become null?”..? In the first example? How could it? It’s inside and dictated by the foreach. IE it wouldn’t even be hit unless there was something there, right?

I will take a look at your article and see what I can learn from it. Unfortunately I don’t have the link so I can’t provide it here. As for finding some code online…I’m not going to apologize for finding something (even if I don’t understand it) and trying to use and learn from it. I have gleaned a great deal this way. I brought it up here to try and learn more. There are a lot of very smart people out there and it seems you certainly count yourself among them. I’ll look into the ideas you mentioned and see what I can figure out but condescension isn’t necessary. No one deserves anything from anyone else here except for mutual respect.

Sergey Alexandrovich Kryukov 22-Jan-12 14:17pm

Sorry, I made a mistake in first quote which I've just fixed. I types "case" instead of your "a cast". As to two other quotes, they are literally what you say. You will see it if you compare by yourself.
I think my questions to you remain valid. You did not explain to use some very essential things.
--SA

Sergey Alexandrovich Kryukov 22-Jan-12 14:22pm

OK, here is the verdict on singleCast == null and the loop in invocation list. If singleCast is never null, the whole loop makes no sense as this is the only selected condition (InvokeRequired should be carried outside loop and is usually true; it is always true for the call from any non-UI thread). You should invoke the whole delegate instance at once: handler.Invoke.
--SA

rleonard55 22-Jan-12 21:10pm

Are you confusing the “syncInvoke !=null” line with the singleCast object being used to iterate through the GetInvocationList? If not you have complely lost me with the “the whole loop makes no sense” bit.

Sergey Alexandrovich Kryukov 22-Jan-12 14:25pm

You still did not share witch use what's the purpose of the whole method. If you want to add some log (notification message/information, whatever) from a non-UI thread and trigger all handlers of some event, this can be done nearly in one single statement.
--SA

rleonard55 22-Jan-12 21:16pm

Alright man you got me here. I’ve explained to the best of my ability what I was hoping to accomplish. If it isn’t clear enough to convey what I’m looking for I’m at a loss. Not saying I’m doing a great job, I’m just not sure what else or how else to say it. I may need to put this away until I can better understand/articulate it.

Sergey Alexandrovich Kryukov 22-Jan-12 14:30pm

And one little advice: please don't try to get into personal issues. All your references to the notions like "apologize", "smart", "count yourself", "deserved", "respect" are completely irrelevant. No one gave you any reason for such concerns yet. Please, let's set them aside.
--SA

rleonard55 22-Jan-12 21:28pm

Truthfully I may have put more on it than you intended, It was late and a long day…But what? You’re not going to quote the “condescension” part along with the rest? :) Seriously though I’m good, hope you are too. If you ignore any confusing or issued parts to my logic/code in the second part is there an easy way to call the singleCast delegate (like a void) that would put the compiler issue commented about to rest? singleCast(this, logEA) works fine in the first example but when I changed things in the second part singleCast is a variable instead of a method. Seriously I’m not certain I’m making any more sense than before, if not just disregard.

rleonard55 22-Jan-12 21:39pm

*UPDATE* I F'd this up completely I jacked up one very important word in the original post I said I was trying to avoid a "cast" in the form logic. That was completely wrong. I'm trying to avoid a "invoke" in the form logic. That's why I mentioned threads. Sorry I hope that clears things up a bit.

BillWoodruff 22-Jan-12 10:47am

SAK is absolutely spot-on here that we can't really understand what your problem is without seeing your custom EventArgs class. Every custom EventArgs must inherit from EventArgs: that's a requirement. But, within your custom EventArgs, you can define strongly typed variables, and then access them ... without casting ... in the EventHandler ... from the instance of the custom EventArgs passed to the EventHandler.

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