Populate Generic List from GridView with TextBox in ASP.Net

This Way:

<form id="form1" runat="server">
<div>
    <asp:GridView ID="GridView1" HeaderStyle-BackColor="#3AC0F2" HeaderStyle-ForeColor="White"
        runat="server" AutoGenerateColumns="false">
        <Columns>
            <asp:TemplateField HeaderText="UserName">
                <ItemTemplate>
                    <asp:TextBox ID="txtUserName" runat="server" Text='<%# Eval("UserName") %>' />
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="FirstName">
                <ItemTemplate>
                    <asp:TextBox ID="txtFirstName" runat="server" Text='<%# Eval("FirstName") %>' />
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="LastName">
                <ItemTemplate>
                    <asp:TextBox ID="txtLastName" runat="server" Text='<%# Eval("LastName") %>' />
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="Location">
                <ItemTemplate>
                    <asp:TextBox ID="txtLocation" runat="server" Text='<%# Eval("Location") %>' />
                </ItemTemplate>
            </asp:TemplateField>
        </Columns>
    </asp:GridView>
    <asp:Button Text="Save" OnClick="Save" runat="server" />
</div>
</form>

C#:

public class UserDetails
{
    string userName = string.Empty;
    string firstName = string.Empty;
    string lastName = string.Empty;
    string location = string.Empty;

    public string UserName
    {
        get { return userName; }
        set { userName = value; }
    }

    public string FirstName
    {
        get { return firstName; }
        set { firstName = value; }
    }

    public string LastName
    {
        get { return lastName; }
        set { lastName = value; }
    }

    public string Location
    {
        get { return location; }
        set { location = value; }
    }
}

protected void Page_Load(object sender, EventArgs e)
{

    if (!this.IsPostBack)
    {
        DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[4] { new DataColumn("UserName", typeof(string)),
                        new DataColumn("FirstName", typeof(string)),
                        new DataColumn("LastName",typeof(string)),
                        new DataColumn("Location",typeof(string))});
        dt.Rows.Add("John Hammond", "John ", "Hammond", "United States");
        dt.Rows.Add("Mudassar Khan", "Mudassar", " Khan", "India");
        dt.Rows.Add("Suzanne Mathews", "Suzanne", " Mathews", "France");
        GridView1.DataSource = dt;
        GridView1.DataBind();
    }
}

protected void Save(object sender, EventArgs e)
{
    List<UserDetails> userDetails = new List<UserDetails>();
    UserDetails userDetail = new UserDetails();
    foreach (GridViewRow row in this.GridView1.Rows)
    {
        userDetail.UserName = (row.FindControl("txtUserName") as TextBox).Text;
        userDetail.FirstName = (row.FindControl("txtFirstName") as TextBox).Text;
        userDetail.LastName = (row.FindControl("txtLastName") as TextBox).Text;
        userDetail.Location = (row.FindControl("txtLocation") as TextBox).Text;
        userDetails.Add(userDetail);
    }

}

Namespace

using System.Data;