Re: How to unregister an event - C# Discussion Boards

How to unregister an event

19-Jul-07 3:45

Hi Geert,

you got us confused now; at one time you said showing the ComboBox was slow
(I assumed then it was not dropped down, so basically showing an empty TextBox+Arrow,
and clicking it resulted in a very slow dropping down); but now you say
showing the form itself is slow.

Confused | :confused:

depending on which it is, seems to me the splash screen might not be involved at all.

PS: I should have posted this message first, before the one right above it !

Luc Pattyn

try { [Search CP Articles] [Search CP Forums] [Forum Guidelines] [My Articles] }
catch { [Google] }

t4ure4n19-Jul-07 1:51

t4ure4n

19-Jul-07 1:51

I have a procject in which i am using a custom webclient.

I have following event _WebClient.DocumentComplete which i can register and it works.

Now if I want to unregister the first event handler and assign a new event handler I gives me error because I can't use

_WebClient.DocumentComplete = null;

Can some 1 tell me how to unregister the event

o O º(`'·.,(`'·., ☆,.·''),.·'')º O o°
»·'"`»* *☆ t4ure4n ☆* *«·'"`«
°o O º(,.·''(,.·'' ☆`'·.,)`'·.,)º O o°

kubben19-Jul-07 2:00

kubben

19-Jul-07 2:00

When you add an event handler you use +=
to remove one you use -=

_WebClient.DocumentComplete -= new EventHandler(yourEventHandlerNameHere);

Hope that helps.
Ben

Luc Pattyn19-Jul-07 2:01

19-Jul-07 2:01

Hi,

you can undo

someEvent+=new SomeEventHandler(myHandler);

with the following magical line:

someEvent-=new SomeEventHandler(myHandler);

The magic is you create a new object to remove an old (but very similar) object !

Smile | :)

Luc Pattyn

try { [Search CP Articles] [Search CP Forums] [Forum Guidelines] [My Articles] }
catch { [Google] }

Dan Neely19-Jul-07 2:19

Dan Neely

19-Jul-07 2:19

Luc Pattyn wrote:
The magic is you create a new object to remove an old (but very similar) object !

I'd always thought you needed to save the old one to unregister it. Learn something new everyday. Smile | :)

How does this work if buggy code results in the same handler being registered twice?

--
You have to explain to them [VB coders] what you mean by "typed". their first response is likely to be something like, "Of course my code is typed. Do you think i magically project it onto the screen with the power of my mind?" --- John Simmons / outlaw programmer

Luc Pattyn19-Jul-07 2:35

19-Jul-07 2:35

Dont know, havent seen it spec'd, so I can only suggest you try it.
I can confirm if you register twice, you execute twice (that is a common bug, that
harms performance and is not always apparent).

Smile | :)

Luc Pattyn

try { [Search CP Articles] [Search CP Forums] [Forum Guidelines] [My Articles] }
catch { [Google] }

Bijesh19-Jul-07 3:56

Bijesh

19-Jul-07 3:56

dan neely wrote:
How does this work if buggy code results in the same handler being registered twice?

Its ugly. You basically get the same handler invoked twice on that event.. I've had to track down so many of these 'event leaks'.. Sigh | :sigh:

Luc Pattyn19-Jul-07 5:32

19-Jul-07 5:32

Hi Dan,

I ran a little test:

private int clicks=0;
private int handlers=0;
Button btn=new Button();

public override void Run(int arg) {
    doClick();
    addHandler();
    doClick();
    addHandler();
    doClick();
    removeHandler();
    doClick();
    removeHandler();
    doClick();
    removeHandler();
    doClick();
}

void doClick() {
    log("CLICK");
    btn.PerformClick();
}

void addHandler() {
    handlers++;
    log("ADD HANDLER "+handlers);
    btn.Click+=new EventHandler(btn_Click);
}

void removeHandler() {
    log("REMOVE HANDLER "+handlers);
    handlers--;
    try {btn.Click-=new EventHandler(btn_Click);
    } catch { log("failed to remove handler"); }
}

void btn_Click(object sender, EventArgs e) {
    clicks++;
    log("  got click "+clicks);
}

and it resulted in the following log:

15.109     CLICK
15.125     ADD HANDLER 1
15.140     CLICK
15.156       got click 1
15.203     ADD HANDLER 2
15.218     CLICK
15.296       got click 2
15.312       got click 3
15.328     REMOVE HANDLER 2
15.343     CLICK
15.343       got click 4
15.437     REMOVE HANDLER 1
15.468     CLICK
15.484     REMOVE HANDLER 0
15.593     CLICK

So each -= effectively removes exactly one matching delegate if it finds one,
and does not throw otherwise.

Smile | :)

Luc Pattyn

try { [Search CP Articles] [Search CP Forums] [Forum Guidelines] [My Articles] }
catch { [Google] }

Luc Pattyn24-Jul-07 6:46

24-Jul-07 6:46

Hi Dan,

FYI: I just finised turning this subject into a short article. You may want to skim it.

Regards

Luc Pattyn

try { [Search CP Articles] [Search CP Forums] [Forum Guidelines] [My Articles] }
catch { [Google] }

Martin#19-Jul-07 2:33

Martin#

19-Jul-07 2:33

Hello Luc,

Luc Pattyn wrote:
The magic is you create a new object to remove an old (but very similar) object !

I remember that Scott Dorman once pointed out that it is even possible without creating an new object (I think only in .Net>1.1)

Here is the thread![^]

P.S.: This was my Nr.:1000 post.

All the best,

Martin

Luc Pattyn19-Jul-07 2:38

19-Jul-07 2:38

Hi Martin,

I did remember that thread; I havent tried it yet, I still tend to write code that
runs also on 1.1

Martin# wrote:
This was my Nr.:1000 post

Aha, that explains a few things. Now take that holiday !

Smile | :)

Luc Pattyn

try { [Search CP Articles] [Search CP Forums] [Forum Guidelines] [My Articles] }
catch { [Google] }

Martin#19-Jul-07 2:48

Martin#

19-Jul-07 2:48

Luc Pattyn wrote:
Aha, that explains a few things. Now take that holiday !

All the best,

Martin

b_umika19-Jul-07 2:01

b_umika

19-Jul-07 2:01

Have you tried using

_WebClient.DocumentComplete -= <your assigned="" event="" handler="" to="" be="" removed="">;

Is that what you are talking about?

Generating a program ID

Muntyness19-Jul-07 1:49

Muntyness

19-Jul-07 1:49

I have a quick question.

I have a program, and I need every instance of the program to have it's own uniqure ID. (E.G the first one opened has and ID of 12345, the second one has an ID of 74982, etc.)

At the moment the only way I can see of doing this is getting the process ID.

Is this the best way of doing it or are there other, better, ways of generating a unique ID?

- Munty

ekynox19-Jul-07 2:04

ekynox

19-Jul-07 2:04

Why not just use the random number generator and use the current system time as the seed generator. This ought to guarantee a unique sequence of numbers all the time. Or generate a GUID

Luc Pattyn19-Jul-07 2:04

19-Jul-07 2:04

Process ID is just fine; it is unique in that no two processes can be running simultaneously
on the same Windows PC unless their processIDs are different.

Why bother to try and come up with some other unique number ?

Smile | :)

Luc Pattyn

try { [Search CP Articles] [Search CP Forums] [Forum Guidelines] [My Articles] }
catch { [Google] }

Chintan.Desai19-Jul-07 2:29

Chintan.Desai

19-Jul-07 2:29

yup,if it is working with single process class which gurantee to be unique, then y to use time or random class.

Regards
Chintan
www.visharadsoft.com
(Nothing is so purify as KNOWLEDGE)

Creating directory trees with 1M nodes

Muntyness19-Jul-07 6:50

Muntyness

19-Jul-07 6:50

Alrighty then, I guess I'll just stick with the Process ID.

Thansk All.

- Munty

ss4219-Jul-07 1:44

ss42

19-Jul-07 1:44

Apologies in advance that may not be a C# issue, but perhaps .NET, NTFS, XP-SP2 or even hardware. You tell me.

I have sucessffuly ran breath-first and depth-first versions of the following C# snippet on different hardware as a precursor to noodling around with databases, SQLite, etc. Seems simple enough. Makes 1M diretcories as in D:dataset/II/JJ/KK where II, JJ, and KK are are 100 nodes each. On my developmemt machine (xp-sp2, 2GB, stable) I have this repeatable condition where when I get to about i = 67 (670K dirs created) the program slows down and then the system becomes unresponsive enough that I must reboot! No chance to use the VS debugger.

I quick format the D: drive before each operation, so the dir construction in this program is being performed on a clean FS with a new MFT. I watch the memory usage (doesn't use much). I've monitored the heap (doesn't use much). I'm perplexed with this system-specific issue; as it is one of the few times (for me) that a user-space program has caused so much trouble. Thoughs on what to try next appreacited. Or pointers to a more appropriate forum. (Yes, I know I should try/catch a possible exception at CreateDirectory; I doubt that is the issue). Thanks!

namespace make_dir_tree
{
class Program
{
static void Main(string[] args)
{
string path;

Stopwatch watch = new Stopwatch();
watch.Start();

for (int i = 0; i < 100; i++)
for (int j = 0; j < 100; j++)
{
for (int k = 0; k < 100; k++)
{
path = String.Format("D:/dataset/{0:D2}/{1:D2}/{2:D2}", i, j, k);
Directory.CreateDirectory(path);
}
Console.WriteLine("i:{0} j:{1}",i,j);
}

watch.Stop();
Console.WriteLine("Elapsed: {0}", watch.Elapsed);
Console.WriteLine("In milliseconds: {0}", watch.ElapsedMilliseconds);
}
}
}

Re: Creating directory trees with 1M nodes

Luc Pattyn19-Jul-07 2:20