Deleting items in listview if data already exists - vb.net

Question

i'am populating my listview and when i click the command button the data will be saved to database but if a data already exists in the database the data will be removed from my listview. my problem is that when the data already exists yes it removes the data but it always leave 1 data in my listview. for example i populate my list with 10 data that already exist in database and when i press the command button since its already in the database it will delete the 10 data in my listview what happens is it leaves the last data in the listview
Dim ListOfExistingItem As List(Of Integer) = New List(Of Integer)
Try
locconn.Open()
For x = 0 To ListView2.Items.Count - 1
Dim a As String = ListView2.Items.Item(x).Text
a = ListView2.Items.Item(x).Text
Dim command As New SqlCommand
Dim TMP_SQL_VAL As String = "select count([Check-Out]) from tbl_list1 where barcode = '" + a + "'"
command = New SqlCommand(TMP_SQL_VAL, locconn)
Dim READER As SqlDataReader
READER = command.ExecuteReader()
READER.Read()
If READER(0) = 0 Then
MsgBox("Barcode: " & a & "is still Inside", MsgBoxStyle.Exclamation)
TextBox4.Text = Nothing
ListOfExistingItem.Add(x)
READER.Close()
End If
READER.Close()
Next
If Not IsNothing(ListOfExistingItem) Then
For Each x As Integer In ListOfExistingItem
If Not x >= ListView2.Items.Count - 1 Then
ListView2.Items.RemoveAt(x)
End If
Next
End If

Answer 1

I think your problem is a little more complex than an off-by-1 error.
When you loop through ListOfExistingItem, which should contains the indexes of items to be removed, you are removing items from ListView2.
The problem with this is that by removing an item from the list, you are changing the position of all items after it.
For example, take the list { a, b, c }. The index of 'a' is 0, 'b' is 1, and 'c' is 2.
Now, if you were to say list.RemoveAt(1) then it would remove 'b'. This will then cause the index of 'c' to change to 1 instead of two. Then when you go and try to remove 'c', it wont be in the same place.
For an quick fix, try adding 'ListOfExistingItem.Reverse' before the last 'for' loop:
Call ListOfExistingItem.Reverse()
For Each x As Integer In ListOfExistingItem
If Not x >= ListView2.Items.Count - 1 Then
ListView2.Items.RemoveAt(x)
End If
Next
This way, you will start with the last item in the list and work your way backwards, which should avoid the problem.