Delete from list using foreach using listbox selected item

Question

I am trying to use this method that is ran from a button click that will retrieve the select item from a listbox then remove this item from the list. Whenever i run the code i get this error: "List that this enumerator is bound to has been modified. An enumerator can only be used if the list does not change.".

I'm completely stumped.

    public void DeleteSale()
    {
        foreach (BootSale b in lstBootSales.SelectedItems)
        {

            lstBootSales.Items.Remove(b.Id);
            lstBootSales.Items.Remove(b.Date);

            DisplayAllBootSales();
        }
    }

DisplayAllBootSales();simply refreshes the listbox values afterwards

I have a List "BootSale" where I store information which is written to a listbox. I want to be able to click the item in the listbox then click delete and it will be completely removed from the system

You can't modify a collection while enumerating through it.

MarcinJuraszek
– MarcinJuraszek

2013-02-28 14:43:03 +00:00
Commented Feb 28, 2013 at 14:43 — MarcinJuraszek
– MarcinJuraszek, Commented Feb 28, 2013 at 14:43
What does DisplayAllBootSales do?

bash.d
– bash.d

2013-02-28 14:43:55 +00:00
Commented Feb 28, 2013 at 14:43 — bash.d
– bash.d, Commented Feb 28, 2013 at 14:43
@bash.d Display all boot sales?

DGibbs
– DGibbs

2013-02-28 14:51:05 +00:00
Commented Feb 28, 2013 at 14:51 — DGibbs
– DGibbs, Commented Feb 28, 2013 at 14:51
@DGibbs Thanks, Captain Obvious!

bash.d
– bash.d

2013-02-28 14:51:47 +00:00
Commented Feb 28, 2013 at 14:51 — bash.d
– bash.d, Commented Feb 28, 2013 at 14:51
Ask a stupid question, get a stupid answer.

DGibbs
– DGibbs

2013-02-28 14:53:14 +00:00
Commented Feb 28, 2013 at 14:53 — DGibbs
– DGibbs, Commented Feb 28, 2013 at 14:53

Eduard Dumitru · Accepted Answer · 2013-02-28 16:03:04Z

2

do this:

class Foo {

    BootSaleList bootsalelist;

    public void DeleteSale()
    {
        foreach (BootSale b in lstBootSales.SelectedItems.OfType<BootSale>().ToArray())
        {
            //temp.Remove(b); -- no more of this guy
            bootsalelist.ReturnList().Remove(b);
            lstBootSales.Items.Remove(b);

            // and no more of these guys:

            //lstBootSales.Items.Remove(b.Id); 
            //lstBootSales.Items.Remove(b.Date);
            //DisplayAllBootSales();
        }
    }

 }

where:

[Serializable]
public class BootSaleList : IDisplay
{
    private List<BootSale> bootsales;

    public List<BootSale> ReturnList()
    {
        return bootsales;
    }
}

and it will work perfectly

edited Feb 28, 2013 at 16:03

answered Feb 28, 2013 at 14:43

Eduard Dumitru

3,25019 silver badges32 bronze badges

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10 Comments

Liamc3000 Over a year ago

thanks for help tried this but get the error "Cannot convert type 'System.Windows.Forms.ListViewItem' to 'Bootsale_project.BootSale'"

Liamc3000 Over a year ago

Code now runs fine but it simply deletes the content of the listbox and not the actual list

Eduard Dumitru Over a year ago

And that is precisely what yours would've done if it would not have crashed with the exception...

Liamc3000 Over a year ago

I apologise I maybe wasnt clear at first I have a List "BootSale" where I store information which is written to a listbox. I want to be able to click the item in the listbox then click delete and it will be completely removed from the system.

Eduard Dumitru Over a year ago

I have to ask how it is possible that SelectedItems which is a subset of Items contain things whose properties (Id and Date) are contained in Items (for which it would be a good idea to delete them from Items). I really thought you were asking about the error "List that this enumerator is bound to has been modified. An enumerator can only be used if the list does not change." and that your code was just a sample... Is that error gone or not ? Are you asking how to actually do it ? Look at my latest edit. Personally I really don't understand the removing of .Id and .Date...

|

Matt Burland · Accepted Answer · 2013-02-28 14:43:05Z

2

The error message says it all. You can't remove items from a list you are iterating over. You must remove the items outside of the foreach loop. One simple fix is to use a regular for loop instead.

answered Feb 28, 2013 at 14:43

Matt Burland

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Comments

M ten Klooster · Accepted Answer · 2013-02-28 15:30:09Z

1

Best way to do this is looping the list Top - Down (instead of down - top)

for(int i = YourListItems.Count(); i > 0; i--)
{
    // Remove from list
}

This way will prevent any index errors.

Goodluck

edited Feb 28, 2013 at 15:30

answered Feb 28, 2013 at 14:54

M ten Klooster

3512 silver badges4 bronze badges

Comments

DGibbs · Accepted Answer · 2013-02-28 14:44:14Z

0

You cannot modify a collection from within a foreach, you could however use a temporary list, something along the lines of:

public void DeleteSale()
{
    List<T> temp = lstBootSales;
    foreach (BootSale b in lstBootSales.SelectedItems)
    {
        temp.Items.Remove(b.Id);
        temp.Items.Remove(b.Date);

        DisplayAllBootSales();
    }

    lstBootSales = temp;
}

answered Feb 28, 2013 at 14:44

DGibbs

14.7k7 gold badges49 silver badges89 bronze badges

Comments

VladL · Accepted Answer · 2013-02-28 14:47:31Z

0

Looking on your code I might assume, that lstBootSales holds a list of BootSale. But you are trying to delete something different than BootSale. Also use for instead of foreach:

        for (int i = 0; i < lstBootSales.SelectedItems.Count; i++)
        {
            lstBootSales.Items.Remove(lstBootSales.SelectedItems[i]);

            DisplayAllBootSales();
        }

answered Feb 28, 2013 at 14:47

VladL

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