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Removing an item from a list c#

I am having trouble with removing an item from a list in c#. My current code is below:
for (int i = current.Count - 1; i >= 0; i--)
{
foreach (ListItem li in sp_list.Items)
{
if (li.Text == current[i].uname)
{
current.RemoveAt(i);
}
}
}
The aim of the code is to compare the existing items in a list box with newly added items so I know which items have just been added. So currently I am getting the current list box items from the database (they are stored here, it is a databound list box), entering these into a list and for each of the list items, comparing them with the items in a list box and if they match, remove the item from the list.
Therefore, in the end, if I add two new entries, the list should only be storing the two newly added values.
The code does not work as the first item is removed fine, but then, the value of i is greater than current.count - and therefore I get an out of range exception!
Could someone help me with this issue? Apologies about the confusing question, it's hard to explain! Thanks

You can do it with Linq. Not sure if casting to ListItem needed (you can remove it)
current.RemoveAll(x => sp_list.Items.Cast<ListItem>()
.Any(li => li.Text == x.uname));

Once you've found the matching value, and removed it from the list, you want to break out of the inner loop to check the next item.
if (li.Text == current[i].uname)
{
current.RemoveAt(i);
break;
}

Your nesting is wrong, I think you wanted,
foreach (ListItem li in sp_list.Items)
{
for (int i = current.Count - 1; i >= 0; i--)
{
if (li.Text == current[i].uname)
{
current.RemoveAt(i);
}
}
}
alternatively, use linq,
// For lookup performance.
var items = new HashSet(sp_list.Items.Select(i => i.text));
current = current.Where(c => !items.Contains(c.uname)).ToList();

How about this:
foreach (ListItem li in sp_list.Items) {
if (current.Contains(li.Text)) {
current.Remove(li.Text);
}
}

Put a break statement after the RemoveAt so you don't remove that item again.

you can travel the list in reverse order and remove items using RemoveAt(i).
also for efficiency purposes you may want to put the ListItem texts in a Set so you can don't have to loop though the sp_list.Items for each of your current items.

How to delete many items in listbox?

how to delete from listbox ?
deleting many indexes at the same time
Note that im using list of car types with their details
the objects in the listBox have car type cost rate

Update: If you want to remove all selected items as commented:
foreach (int i in listBox1.SelectedIndices)
listBox1.Items.RemoveAt(i);
If you want to delete all items instead, use Clear:
listBox1.Items.Clear();
if you want to remove at a specific index, use RemoveAt:
listBox1.Items.RemoveAt(0);
or in a loop:
for(int i = 0; i < listBox1.Items.Count; i++)
listBox1.Items.RemoveAt();
if you want to remove a speicific item, use Remove:
Car car = (Car) listBox1.Items[0];
listBox1.Items.Remove(car);

You have to use loop.
Something like this:
List<int> indexesToDelete = new List<int>();
// add items you want to remove to List like this:
indexesToDelete.Add(1);
indexesToDelete.Add(2);
indexesToDelete.Add(4);
// loop will execute code inside inside for all items added to list
foreach (int indexToDelete in indexesToDelete)
{
listbox1.RemoveAt(indexToDelete);
}
Edit: itemsToDelete renamed to indexesToDelete in code.

replacing an object in listview with new one?

I have a listview with few items. I am using foreach loop to check if there is a match. The code I am using looks like this:
foreach (ListViewItem test in listView1.Items)
{
if (test.SubItems[1].ToString() == item.SubItems[1].ToString())
{
test.Tag = item.Tag;
}
}
What I am trying to do is, check the 2nd index and if there is a match replace the old item 'test' with the new one 'item'.
Apparently there is no change in the listview. Is the way I am replacing the object wrong?

you can clone the item and assign directly to the list view item. but you need to change foreach loop to for loop.
for (int i = 0; i < listView1.Items.Count; i++)
{
if (listView1.Items[i].SubItems[1].ToString() == item.SubItems[1].ToString())
{
listView1.Items[i] = (ListViewItem)item.Clone();
}
}

You have updated the Tag only. You need to change test.SubItems[0], test.SubItems[1],... to see the changes.
Or you could remove old item and insert new item by using listView1.Items.Remove(...) or listView1.Items.RemoveAt(...) and listView1.Items.Insert(...). But if you need to pay account of performance you should use the first algorithm (changing test.SubItems[i]).

Check all item in listview with huge list item?

I want to check about 3000 item in listview. This is a bit of code :
foreach (ListViewItem item in this.lvItem.Items)
{
item.Checked = !item.Checked;
}
But listview is very slow when item is checked. Please give me some ideas to solve this problem? Thanks.

I had the same problem but I found why.
I had an "ItemChecked" event handler attached to my listView that was doing some heavy stuff.
I removed the eventHandler and it solved my problem.
Try removing any "ItemChecked" eventhandler and see if the speed is better.

You need to call BeginUpdate before the loop and EndUpdate after the loop:
listView1.BeginUpdate();
foreach (ListViewItem item in listView1.Items)
item.Checked = true;
listView1.EndUpdate();
Calling BeginUpdate prevents the control from drawing until the EndUpdate method is called.

I heard a rumor that for large list items a for loop will work faster than a foreach loop
try
for(int i = 0; i = < this.1vItem.Items.Count; i++)
{
//Stuff
}

I also don't think it's wise to expect a user to click 3000 items. But something I did recently, when adding the items, knowing that there would never be many and by default they should be checked, is check the items before adding them to the list.
Something like this:
foreach (Recipient recipient in recipients)
{
var item = new ListViewItem(recipient.FirstName + " " + recipient.LastName);
item.Tag = recipient;
item.Checked = true;
lvRicipients.Items.Add(item);
}

Will something like this work for you? ...when checked, add the items to a Dictionary ...when unchecked, remove from the Dictionary. Not tested code but wondering if you could do something like this:
Dictionary<String, ListViewItem> Dic = listView.Items
.Cast<ListViewItem>()
.ToDictionary(x => x.Text, x => x.SubItems[0].Checked);
You asked how to better go about it. What I am saying is on your Check Event you will want to add items to your list view. I doubt that a user will actually check all 3000, so change your code to decide how you would want to handle checked items, the example that I have given you uses Lambda expression. If not familiar, then please alter your question to reflect what it is that you actually need and/or want...

for (int i = 0; i <= listView1.Items.Count - 1; i++)
{
if (!listView1.Items[i].Checked)
listView1.Items[i].Checked = true;
}

Safely remove list from list in loop

I am iterating through all the list in mainlist and if a specific condition occur. I want to remove that specific list.
It is not working.
for (int i = 0; i < mainList.Count; i++)
{
if (mainList[i].Dead == true) //
{
mainList.removeAt(i);//what will be affect on mainList.Count;
}
}

mainList.RemoveAll(x => x.Dead);

The way you constructed your for loop, it will only work if mainList.Count stays constant, but you are removing elements during your loop. Do you understand why that is a problem? Whenever you remove an element you end up skipping the check of the element after it.
I think you could use foreach and mainList.remove but I'm not sure. Another solution is to just make your loop count downwards:
for (int i = mainList.Count-1; i >= 0; i--)
{
if (mainList[i].Dead == true)
{
mainList.removeAt(i);
}
}

You will not be able to do that since you are altering the length of the list when you are doing so. I would do it like this instead:
var newList = mainList.Where(y => !y.Dead).ToList();

How to modify or delete items from an enumerable collection while iterating through it in C#
http://bytes.com/topic/c-sharp/answers/238241-how-do-you-modify-array-while-iterating-through