Как экспортировать все элементы checkledistbox в XML-документ в приложении windows form C#

Im not able to display all checked data in xml document only last selected Checkedlistbox item is displayed in xml i wanted to display all checked data in xml please help me in doing this..

  

What I have tried:

<pre> private void button2_Click(object sender, EventArgs e)
        {
            string str = " ";
            for (int i = 0; i < checkedListBox1.Items.Count; i++)
            {
                if (checkedListBox1.GetItemChecked(i))
                {
                     str = (string)checkedListBox1.Items[i];
                    MessageBox.Show(str);
                }

            }
        System.IO.File.WriteAllText("GetDetails.xml", str);
                XmlTextWriter xwriter = new XmlTextWriter("GetDetails.xml", Encoding.Unicode);
                xwriter.WriteStartDocument();
                xwriter.WriteStartElement("XMLFILE");
                xwriter.WriteStartElement("file");
                xwriter.WriteString(textBox1.Text);
                xwriter.WriteEndElement();
                // xwriter.WriteAllText(" ");
                foreach (String item in checkedListBox1.SelectedItems)
                {
                    xwriter.WriteStartElement("SelectedItems");
                    xwriter.WriteString(item);
                    xwriter.WriteEndElement();
                //xwriter.WriteAllText("GetDetails.xml", str);
                // File.WriteAllText("GetDetails.xml", str);
                /*  for (int i = 0; i < checkedListBox1.CheckedIndices.Count; i++)
                  {
                      //checkedListBox1.ClearSelected();
                      checkedListBox1.Items.Add(checkedListBox1.CheckedIndices[i]);
                  }*/
            }
            //File.WriteAllText("GetDetails.xml", str);
            xwriter.WriteEndElement();
                xwriter.WriteEndDocument();
                xwriter.Close();

            }