ListBoxコントロールは、上へ移動、下へ移動、循環上へ移動、循環下へ移動操作を実現する

<style type="text/css">
    .left {
        float:left;
        width:120px;
        
    }
    .right {
        float:right;
        width:80px;
    }
    .all {
        width:200px;
    }
</style>

 protected void Button1_Click(object sender, EventArgs e)
    {
        //ListBox1.Items.Remove(ListBox1.SelectedItem);   
        //             
        if (ListBox1.SelectedIndex > 0) {
            int idx = ListBox1.SelectedIndex;
            ListBox1.Items.Insert(ListBox1.SelectedIndex - 1, ListBox1.SelectedItem.ToString());
            ListBox1.Items.RemoveAt(ListBox1.SelectedIndex);
            ListBox1.SelectedIndex = idx - 1;
        }
     }

    protected void Button2_Click(object sender, EventArgs e)
    {
        //  
        if (ListBox1.SelectedIndex < ListBox1.Items.Count - 1)
        {
            ListBox1.Items.Insert(ListBox1.SelectedIndex, ListBox1.Items[ListBox1.SelectedIndex + 1].ToString());
            ListBox1.Items.RemoveAt(ListBox1.SelectedIndex + 1);
        }
    }

    protected void Button3_Click(object sender, EventArgs e)
    {
        //    
        if (ListBox1.SelectedIndex == 0) {
            ListBox1.Items.Insert(ListBox1.Items.Count,ListBox1.SelectedItem.ToString());
            ListBox1.Items.RemoveAt(ListBox1.SelectedIndex);
        }
    }

    protected void Button4_Click(object sender, EventArgs e)
    {
        //    
        if (ListBox1.SelectedIndex == ListBox1.Items.Count-1) {
            ListBox1.Items.Insert(0, ListBox1.SelectedItem.ToString());
            ListBox1.Items.RemoveAt(ListBox1.SelectedIndex);
        }
    }