Collection was modified; enumeration operation may not execute.

Question

4.00/5 (2 votes)

See more:

Hello,
I am running into the following error:

Collection was modified; enumeration operation may not execute.

I have a collection that gets modified

Here is the code;

C#

foreach (var m in newSpectrum.PeakCentroids)
                {
                    newSpectrum.PeakCentroids.Remove(m);
                                 }

How do I get around this error?

Posted 23-Jul-11 19:31pm

shekarchee

Add a Solution

Comments

RaisKazi 24-Jul-11 2:13am

Error is obvious. You are Removing items from the collection, which is traversing through "foreach" loop.

Sergey Alexandrovich Kryukov 24-Jul-11 2:26am

Correct, I would vote 5.
--SA

Sergey Alexandrovich Kryukov 24-Jul-11 2:37am

Actually, you explained what was wrong, I added a solution showing how to work around this problem, please see.
--SA

manjudk44 11-Jul-12 6:04am

Collection was modified; enumeration operation may not execute.same error coming while using above code...help me to get the solution...
I am added gridview...want to bind some subject on each date of a month..

manjudk44 11-Jul-12 6:05am

protected void Calender1_DayRender(object sender, DayRenderEventArgs e)
{
if (e.Day.DayNumberText == "1" | e.Day.DayNumberText == "2" | e.Day.DayNumberText == "3" | e.Day.DayNumberText == "4" | e.Day.DayNumberText == "5" | e.Day.DayNumberText == "6" | e.Day.DayNumberText == "7" | e.Day.DayNumberText == "8" | e.Day.DayNumberText == "9" | e.Day.DayNumberText == "10" | e.Day.DayNumberText == "11" | e.Day.DayNumberText == "12" | e.Day.DayNumberText == "13" | e.Day.DayNumberText == "14" | e.Day.DayNumberText == "15" | e.Day.DayNumberText == "16" | e.Day.DayNumberText == "17" | e.Day.DayNumberText == "18" | e.Day.DayNumberText == "19" | e.Day.DayNumberText == "20" | e.Day.DayNumberText == "21" | e.Day.DayNumberText == "22" | e.Day.DayNumberText == "23" | e.Day.DayNumberText == "24" | e.Day.DayNumberText == "25" | e.Day.DayNumberText == "26" | e.Day.DayNumberText == "27" | e.Day.DayNumberText == "28" | e.Day.DayNumberText == "29" | e.Day.DayNumberText == "30" | e.Day.DayNumberText == "31")
{
if (e.Day.Date.DayOfWeek != DayOfWeek.Sunday)
{
if (!(e.Day.IsOtherMonth))
{
dt = new DataTable();
dt = obj_calender.load_basedonsubject();
GridView1.DataSource = dt;
GridView1.DataBind();
GridView1.HeaderRow.Visible = false;
e.Cell.Font.Italic = true;
e.Cell.Font.Size = FontUnit.Small;
e.Cell.Controls.Add(GridView1);
e.Cell.Width = 50;
e.Cell.Height = 50;
e.Day.IsSelectable = false;
}
}
}
}

manjudk44 11-Jul-12 6:06am

Collection was modified; enumeration operation may not execute.same error coming while using above code...help me to get the solution...
I am added gridview...want to bind some subject on each date of a month..

4 solutions

Solution 3

If the Collection is fairly small and performance is not the most important need, you can do it this way:

C#

foreach (var m in newSpectrum.PeakCentroids.ToList())
{
    newSpectrum.PeakCentroids.Remove(m);
}

Posted 23-Jul-11 21:50pm

dan!sh

Solution 4

let see if this can help:

C#

//get key collection from dictionary into a list to loop through
List<int> keys = new List<int>(Dictionary.Keys);

// iterating key collection using simple for-each loop
foreach (int key in keys)
{
    // Now we can perform any modification with values of dictionary.
    Dictionary[key] = Dictionary[key] - 1;

}

Resolved Collection Error

Posted 11-Nov-14 2:42am

open and free

Updated 31-Dec-14 23:47pm

v2

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Sergey Alexandrovich Kryukov · Accepted Answer · 2011-07-23T20:36:00

Most likely, there is a method Clear, so write newSpectrum.PeakCentroids.Clear().

What if you need to remove just part of elements, on some condition? A most universal solution would be:

C#

using CentroidsList = System.Collection.Generic.List<...>; //put the type of the element of newSpectrum.PeakCentroids

//...

CentroidsList list = new CentroidsList();
foreach (var element in newSpectrum.PeakCentroids)
   if (SomeCondition(element))
       list.Add(element);
foreach (var element in list)
   newSpectrum.PeakCentroids.Remove(element);

It depends what collection is that. In many cases you can write more effective code using for with index, not foreach. Traverse the collection in reverse (from Count - 1 to 0) and delete required elements. In this case deletion will not disrupt the loop.

—SA

Abhinav S · Accepted Answer · 2011-07-23T20:40:00

Solution 2

You cannot modify(remove, add items) the collection while looping through it at the same time.
Its as simple as that.

What you can do is loop through the collection, find the item you want to remove, and then remove the item for the collection.
For removing all items, use clear on the collection.

Posted 23-Jul-11 20:40pm

Abhinav S

Updated 23-Jul-11 20:41pm

v3

Comments

RaisKazi 24-Jul-11 3:33am

To the Point. 5.

Abhinav S 24-Jul-11 3:36am

Thanks Rais.