Problem in saving the xml file c# winforms

[EDN Admin]

<pre class="prettyprint using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Xml;
using System.Xml.Linq;

namespace XmlAddDelRecord
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
LoadDatagrid();
}

private void LoadDatagrid()
{
try
{
XmlReader xmlFile;
xmlFile = XmlReader.Create(filePath, new XmlReaderSettings());
DataSet ds = new DataSet();
ds.ReadXml(xmlFile);
dataGridView1.DataSource = ds.Tables[0];
}
catch (Exception ex)
{
MessageBox.Show(ex.ToString());
}
}


private const string filePath = @"C:testPerson.xml";

private void button1_Click(object sender, EventArgs e)
{

var xmlDoc = new XmlDocument();

xmlDoc.Load(filePath);

var subRoot = xmlDoc.CreateElement("Customer");
subRoot.SetAttribute("id", textBox6.Text.Trim());

var firstName = xmlDoc.CreateElement("FirstName");
var xmlTextUserName = xmlDoc.CreateTextNode(textBox1.Text.Trim());
firstName.AppendChild(xmlTextUserName);
subRoot.AppendChild(firstName);
if (xmlDoc.DocumentElement != null) xmlDoc.DocumentElement.AppendChild(subRoot);

var email = xmlDoc.CreateElement("LastName");
var xmlTextEmail = xmlDoc.CreateTextNode(textBox2.Text.Trim());
email.AppendChild(xmlTextEmail);
subRoot.AppendChild(email);
if (xmlDoc.DocumentElement != null) xmlDoc.DocumentElement.AppendChild(subRoot);

var mobile = xmlDoc.CreateElement("Mobile");
var xmlTextMobile = xmlDoc.CreateTextNode(textBox3.Text.Trim());
mobile.AppendChild(xmlTextMobile);
subRoot.AppendChild(mobile);
if (xmlDoc.DocumentElement != null) xmlDoc.DocumentElement.AppendChild(subRoot);

var address = xmlDoc.CreateElement("Address");
var xmlTextAddress = xmlDoc.CreateTextNode(textBox4.Text.Trim());
address.AppendChild(xmlTextAddress);
subRoot.AppendChild(address);
if (xmlDoc.DocumentElement != null) xmlDoc.DocumentElement.AppendChild(subRoot);

var country= xmlDoc.CreateElement("Country");
var xmlTextCountry = xmlDoc.CreateTextNode(textBox5.Text.Trim());
country.AppendChild(xmlTextCountry);
subRoot.AppendChild(country);
if (xmlDoc.DocumentElement != null) xmlDoc.DocumentElement.AppendChild(subRoot);

xmlDoc.Save(filePath);
if (File.Exists(filePath)) return;
var textWritter = new XmlTextWriter(filePath, null);
textWritter.WriteStartDocument();
textWritter.WriteStartElement("CustomerRecord");
textWritter.WriteEndElement();

textWritter.Close();
}

//Search record if not found then add a record
private void button3_Click(object sender, EventArgs e)
{
XDocument doc = XDocument.Load(filePath);

string id = textBox6.Text;
XElement element = doc.Descendants("Customer").FirstOrDefault(p => p.Attribute("id").Value == id);

if (element != null)
{
//found
textBox6.Text = textBox6.Text;
textBox1.Text = (string)element.Element("FirstName");
textBox2.Text = (string)element.Element("LastName");
textBox3.Text = (string)element.Element("Mobile");
textBox4.Text = (string)element.Element("Address");
textBox5.Text = (string)element.Element("Country");

}
else
{
//Not found
//To add a customer

var FirstName = textBox1.Text;
var LastName = textBox2.Text;
var Mobile = textBox3.Text;
var Address = textBox4.Text;
var Country = textBox5.Text;

var ele = new XElement("Customer");
ele.SetAttributeValue("id", id);
ele.Add(new XElement("FirstName", FirstName));
ele.Add(new XElement("LastName", LastName));
ele.Add(new XElement("Mobile", Mobile));
ele.Add(new XElement("Address", Address));
ele.Add(new XElement("Country", Country));
if (doc.Root != null) doc.Root.Add(ele);
doc.Save(filePath);
dataGridView1.Refresh();
dataGridView1.Parent.Refresh();
}
}

//To Remove Record
private void button2_Click(object sender, EventArgs e)
{
XDocument doc = XDocument.Load(filePath);
var q = from node in doc.Descendants("Customer")
let attr = node.Attribute("id")
where attr != null && attr.Value == textBox6.Text
select node;
q.ToList().ForEach(x => x.Remove());
doc.Save(filePath);
dataGridView1.Refresh();
dataGridView1.Parent.Refresh();
}
}
}
[/code]
Im working on an example for myself to learn linq and xml writter. I want to create, delete and search data from a XML file. In each function I got a problem "IOException was UnHandlled" `The process cannot access the file C:testPerson.xml because it
is being used by another process.`
Can anybody tell me how do i fix this problem.

Sample XML:
<pre class="prettyprint <CustomerRecord>
<Customer id="6786
<FirstName>khkjh</FirstName>
<LastName>jkhjkh</LastName>
<Mobile>887897</Mobile>
<Address>jk</Address>
<Country>fdgfdg</Country>
</Customer>
</CustomerRecord>[/code]
<br/>


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