Pass the content of listview column[1] to a string.

Hi,
I have a listview which the user can enter data through an input-form. When the user double clicks on the row of the listview the input form appears. But when the user double clicks on the same row the input-form appears twice. I am busy to prevent this.

Every input-form has a label with a date showing and it's a unique value stored in the column 1 of the listview when the user closes the input-form. I want to use that unique value to determine if an certain input-form is allready openend. By creating a list of strings. So when the user opens an input-form the date of the label will be added to the list of strings.

private List<string> opened = new List<string><();

        private void bbNewNote_ItemClick(object sender, DevExpress.XtraBars.ItemClickEventArgs e)
        {
            StickyNotes sticky = new StickyNotes();
            sticky.gpclCaption.Text = "New Note";
            sticky.rtbContent.Clear();
            sticky.lblCreation.Text = (DateTime.Now.ToString());
            opened.Add(sticky.lblCreation.Text);
            sticky.FormClosed += new FormClosedEventHandler(sticky_FormClosed);
            sticky.Show();
        }

Select allOpen in new window

So now I have to write code to determine when the user double clicks on the row of the listview if the input-form allready exists.

        private void lvNotes_DoubleClick(object sender, EventArgs e)
        {
            string selectedId = this.lvNotes.SelectedItems[0].ToString(); <=======
            if (opened.Contains(selectedId)) return;
            OpenSticky(lvNotes.SelectedItems[0]);
        }

Select allOpen in new window

At the line that I have marked with an arrow is the line that is not correct.
In that line i have to pass the content of lvNotes.Column[1] to the string
selectedId.

What do I do wrong?

Greetings, Peter Kiers