How to save checked items of CheckedListBox to retrieve them later?

Question

Controls:

• 1 ComboBox
• 1 CheckedListBox

ComboBox:

• Items: 110
• Events:
  • SelectedIndexChanged: Each time the selected index change the items collection of CheckedListBox change

Functions:

private void cbSubCategories_SelectedIndexChanged(object sender, EventArgs e)
{
    switch(cbSubCategories.Text)
    {
        clbSubCategories2.Items.Clear();
        case "Category 1":
            AddSubCategory(0, 15);
            break;
        //etc.
    }
}

private void AddSubCategories2(int from, int to)
{
    for (int i = from; i < to; i++)
        clbSubCategories2.Items.Add(strSubCategories2[i]);
}

CheckedListBox

• Items: Depends on which item selected in ComboBox
• Events:
  • ItemCheck: Add the checked item to a list

Functions:

List<string> checkedItems = new List<string>();

private void clbSubCategories2_ItemCheck(object sender, ItemCheckEventArgs e)
{
    int idx = 0;
    if (e.NewValue == CheckState.Checked)
        checkedItems.Add(clbSubCategories2.Items[e.Index].ToString());
    else if (e.NewValue == CheckState.Unchecked)
    {
        if (checkedItems.Contains(clbSubCategories2.Items[e.Index].ToString()))
        {
            idx = checkedItems.IndexOf(clbSubCategories2.Items[e.Index].ToString());
            checkedItems.RemoveAt(idx);
        }
    }
}

Now lets say I select item A on ComboBox so the CheckedListBox have now Collection Items Q. I check 2 items from Q and then I select different item from ComboBox B so the Collection Items of CheckedListBox (W) change too. Now if I go back to A, the Collection Items Q is again retrieved back. I want now the 2 items that I checked to be retrieved too. How I can do that?

My idea was something like that (I add this code inside cbSubCategories_SelectedIndexChanged at the end) but it throws this exception Collection was modified; enumeration operation may not execute.:

int x = 0;
foreach (string item in clbSubCategories2.Items)
{
    foreach (string item2 in checkedItems)
    {
        if (item2 == item)
            clbSubCategories2.SetItemChecked(x, true);
    }
    x++;
}

Answer 1

why don't you do it upon SelectedIndexChanged event of your comboBox. That's where you are re-binding everytime your CheckedListBox.

so inside AddSubCategories2(int from, int to), after adding items to your CheckedListBox, again iterate through the items of it and mark all those which exist in the checkedItems list.

private void AddSubCategories2(int from, int to)
{
       for (int i = from; i < to; i++)
        clbSubCategories2.Items.Add(strSubCategories2[i]);

       if(checkedItems!=null)
          foreach(string item in checkedItems)
          { 
              int index=  clbSubCategories2.FindStringExact(item);
              if(index>-1)
                clbSubCategories2.SetItemChecked(index, true);
          }
}