Moving items in a listbox in c#

I am adding file names from a directory in a list box which I am able to add successfully.I then should be able to arrange the files in the list box by selecting a particular item & then moving it up or down.

The below function is an attempt to move the file up. I am trying to copy entire listbox items to an object and selected listbox items to a different object.

Then if button is pressed the selected item should be swapped with the item above to it in the list.

I intend to change the new list and copy the items back to the original listbox.But I am unaware how to copy items from object back to the listbox

The below code does not work

private void plus_Click(object sender, EventArgs e)
    {


        object[] items = new object[listBox1.Items.Count];

        listBox1.Items.CopyTo(items, 0);

        object[] selecteditems = new object[listBox1.SelectedItems.Count];

        listBox1.SelectedItems.CopyTo(selecteditems, 0);

        object[] selectedindices = new object[listBox1.SelectedItems.Count];

        listBox1.SelectedIndices.CopyTo(selectedindices, 0);



       // listBox1.Items.CopyTo(items, 0);

        int upper_index = listBox1.Items.Count - 1;

        for (int i = 0; i < listBox1.Items.Count;i++ )
        {
           if ((i == (int)selectedindices[i])&&(i!=0))
            {
                    object temp = items[i];
                    items[i] = items[i - 1];
                    items[i - 1] = temp;
           }
        }








    }

Copyright Notice：Content Author:「Sudarshan Taparia」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/38951357/moving-items-in-a-listbox-in-c-sharp