Remove selected items from Listbox (ObservableCollection)

Question

I am trying to remove selected items in a ListBox which is bound to ObservableCollection.

var selectedFiles = MyList.SelectedItems;
foreach (cListEntry item in selectedFiles)
{
   _myList.Remove(item);
}

"Collection was modified; enumeration operation may not execute"

What is the proper way of doing this?

http://stackoverflow.com/questions/604831/collection-was-modified-enumeration-operation-may-not-execute — Soner Gönül, Jan 19 '14 at 18:00
Specially, read this comment.. http://stackoverflow.com/questions/604831/collection-was-modified-enumeration-operation-may-not-execute#comment13168776_604843 — Soner Gönül, Jan 19 '14 at 18:12

score 6 · Accepted Answer · answered Jan 19 '14 at 18:16

6

You can't modify the collection while enumerating it as evident from the exception itself.

Explanation:

When you remove item from ObservableCollection, MyList.SelectedItems gets update since ObservableCollecton implement INotifyCollectionChanged. Now, selectedFiles is pointing to same reference which results in modifying it.

Solution

Instead create a new list and enumerate over that so that any change in ObservableCollection doesn't reflect back to list which you are enumerating. This will work:

var selectedFiles = MyList.SelectedItems.Cast<object>().ToList();
foreach (cListEntry item in selectedFiles)
{
   _myList.Remove(item);
}

answered Jan 19 '14 at 18:16

Rohit Vats

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Thank you for the explanation and the solution. I was not aware of that. This also seems to work MyList.SelectedItems.Count != 0){_myList.Remove((cListEntry)MyList.SelectedItems[0]);} – Daniel Jan 19 '14 at 18:41
Yeah in case you want to remove only single item, this will work. – Rohit Vats Jan 19 '14 at 19:04

score 1 · Answer 2 · answered Jan 19 '17 at 22:21

This happens when trying to modify an ObservableCollection<T> that is bound to a ListBox, for example. This is how you deal with that:

ObservableCollection<Employee> itemsToRemove = new ObservableCollection<Employee>();

foreach (Employee item in lsbxNames.SelectedItems)
{
    itemsToRemove.Add(item);
}
foreach (Employee item in itemsToRemove)
{
    ((ObservableCollection<Employee>)lsbxNames.ItemsSource).Remove(item);
}

Create a new ObservableCollection<T> called itemsToRemove, with the same T as your collection you are trying to modify.
Iterate through your nodes of SelectedItems in your ListBox. Add them to itemsToRemove.
Iterate through itemsToRemove. Cast the ListBox ItemsSource to an ObservableCollection<T> and remove the matches in itemsToRemove from it.

Reference: http://docs.telerik.com/devtools/wpf/controls/radgridview/managing-data/deleting-entry

So this would mean you should be able to do this:

ObservableCollection<cListEntry> itemsToRemove = new ObservableCollection<cListEntry>();

foreach (cListEntry item in MyList.SelectedItems)
{
    itemsToRemove.Add(item);
}
foreach (cListEntry item in itemsToRemove)
{
    ((ObservableCollection<cListEntry>)MyList.ItemsSource).Remove(item);
}

I'm not sure what _myList is, but you don't need to modify it. Just go directly to the ListBox.

Remove selected items from Listbox (ObservableCollection)

2 Answers2