I have a bug in foreach loop

[Alvin Bruney]

Error:
Collection was modified; enumeration operation may not execute.

I've dodged this issue for a while now with workarounds but now i want to
stand up and fight.
I don't want to run away from it anymore.
How do I get around tampering with a collection within a loop and keep
iterating. Here is my code:

//Threadwork.Getl ist returns a hash table
foreach(Diction aryEntry key in ThreadWork.GetL ist)
{
lock(ThreadWork .GetList)
ThreadWork.GetL ist.Remove(key. Key.ToString()) ;
}

I know why it is happening, but I don't know how to fix it. I've had the
same issue with operations like this
foreach(listite m li in somelistbox.ite ms)
{
trying to remove 2 li items in succession will throw the same exception
because the collection is modified.
}

I know how to work around it by using an arraylist as a temporary container
but I don't want a work around anymore. I want to fix it. I want to remove
the item and keep iterating without using a secondary container to store the
values. I think that workaround is ineligant, cheap and doesn't promote
robust coding. Yuck!

I'd like some help please.
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[Morten Wennevik]

You can use for loops instead
for(int x = 0; x < list.Count; x++)
{
object o = list[x];
// if o should be removed
{
list.Remove(o);
x--; // to check the same x again since this spot will be filled by
"x+1" and so on
}
}

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[Jon Skeet [C# MVP]]

Morten Wennevik <Mo************ @hotmail.com> wrote:

You can use for loops instead
for(int x = 0; x < list.Count; x++)
{
object o = list[x];
// if o should be removed
{
list.Remove(o);
x--; // to check the same x again since this spot will be filled by
"x+1" and so on
}
}

Another alternative is to iterate from the other end:

for (int x=list.Count-1; x >=0 ; x--)
{
object o = list[x];
// if o should be removed
{
list.RemoveAt(x );
}
}

Note that I've changed list.Remove(o) to list.RemoveAt(x ) as that way
the list doesn't need to search for the object to remove and it means
that the *exact* element will be removed rather than one which is equal
and potentially earlier in the list.

--
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http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Alvin Bruney]

So I guess there is no way to iterate thru a collection and tamper with it
then?
I'm not complaining but it seems like if they can implement edit and
continue, they could have implemented this.

I know this solution, I've used it but I was kinda hoping, praying that the
foreach version was available somehow.

Thanks anyway

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"Morten Wennevik" <Mo************ @hotmail.com> wrote in message
news:oprxwa3fpg hntkfz@localhos t...
You can use for loops instead
for(int x = 0; x < list.Count; x++)
{
object o = list[x];
// if o should be removed
{
list.Remove(o);
x--; // to check the same x again since this spot will be filled by
"x+1" and so on
}
}

--
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

[Alvin Bruney]

yes, but that is really only a work around. There seems to be no way to edit
the collection while iterating thru it since it is read only. We had that
ability in C++ by the way. I'm not starting a new thread here. just saying
that i'll stash that quirk away in the archives of .net faux pas.

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"Jon Skeet [C# MVP]" <sk***@pobox.co m> wrote in message
news:MP******** *************** *@msnews.micros oft.com...

Morten Wennevik <Mo************ @hotmail.com> wrote:

You can use for loops instead
for(int x = 0; x < list.Count; x++)
{
object o = list[x];
// if o should be removed
{
list.Remove(o);
x--; // to check the same x again since this spot will be filled by
"x+1" and so on
}
}

Another alternative is to iterate from the other end:

for (int x=list.Count-1; x >=0 ; x--)
{
object o = list[x];
// if o should be removed
{
list.RemoveAt(x );
}
}

Note that I've changed list.Remove(o) to list.RemoveAt(x ) as that way
the list doesn't need to search for the object to remove and it means
that the *exact* element will be removed rather than one which is equal
and potentially earlier in the list.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Alvin Bruney]

I think I lost something converting the foreach to a for loop. I can no
longer correctly obtain the hash code key thru casting. It's bugging me out.

The previous code
foreach(Diction aryEntry key in ThreadWork.GetL ist) retrieved a hashtable.
The foreach automatically

presented me with the index key for that hashtable. Each key is an index for
an array object of length 19. So i could do this inside the loop.

object[] values = (object[]) ThreadWork.GetL ist[key.Key.ToStrin g()]; to
return the exact object and modify it accordingly

string username o= values[4].ToString() for example, since this array object
contains a lot of user info about the user logged into the system. Well the
for loop took that ability away from me. I need to get it back.

for(int x = 0; x < list.Count; x++)
{
object o = list[x];

returns a null object. I hope i am making sense here.
//relevant declaration
Hashtable AccessTable = new Hashtable()

[snip]

object[] valTable = new object[]{

"Server: "+HttpContext.C urrent.Server.M achineName, ...[snip]

[snip]

AccessTable.Add (si,valTable);

[Michael Petrotta]

"Alvin Bruney" <vapordan_spam_ me_not@hotmail_ no_spamhotmail. com> wrote in message news:<Ox******* ******@tk2msftn gp13.phx.gbl>.. .

yes, but that is really only a work around. There seems to be no way to edit
the collection while iterating thru it since it is read only. We had that
ability in C++ by the way. I'm not starting a new thread here. just saying
that i'll stash that quirk away in the archives of .net faux pas.

You may find this useful:

http://msdn.microsoft.com/library/de...rp01212002.asp

Scroll down to the section headed "Isolation" .

[Alvin Bruney]

this is a broken link

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"Michael Petrotta" <mi************ **@yahoo.com> wrote in message
news:50******** *************** ***@posting.goo gle.com...

"Alvin Bruney" <vapordan_spam_ me_not@hotmail_ no_spamhotmail. com> wrote in message news:<Ox******* ******@tk2msftn gp13.phx.gbl>.. .

yes, but that is really only a work around. There seems to be no way to edit the collection while iterating thru it since it is read only. We had that ability in C++ by the way. I'm not starting a new thread here. just saying that i'll stash that quirk away in the archives of .net faux pas.

You may find this useful:

http://msdn.microsoft.com/library/de...rp01212002.asp
Scroll down to the section headed "Isolation" .