Get Item from GridViewRow ASP.NET

I have a GridView which I Bind a DataSource to it from a SQL Database, the grid has a column with a checkbox in it so I can "select" a few Item in it (Rows actually). What I want here is to do some updates on the Item in each selected rows, but after some search I can't find how to access the Item in a Row, I though DataItem would work, but it's giving me a Null.

Edit: To make it short, I have a GridView which is built from a DataSource, so basically, each rows represent an Object, when I have a checkbox checked in one of the rows, I want to be able to grab the Object related to that Row, what is the easiest way to achieve that?

The DataBinding on Page_Load:

  if (!Page.IsPostBack)
    {
        gvUnusedAccessories.DataSource = currentContext.Items.OfType<Accessory>().Where(ac => ac.Item_Parent_Id == ((PhoneLine)currentItem).Parent.Item_Id);
        gvUnusedAccessories.AutoGenerateColumns = false;
        gvUnusedAccessories.DataBind();
    }

The event when I press the Update Button, It actually browse the rows and if the row has a checked box it's gonna do the update:

protected void btnAddToMobile_Click(object sender, EventArgs e)
{
    foreach (GridViewRow row in gvUnusedAccessories.Rows)
    {
        if(((CheckBox)row.FindControl("chkSelect")).Checked)
        {
            ((Accessory)row.DataItem).PhoneLine_Id = currentItem.Item_Id;
        }
    }
}

And here's my GridView in the .aspx :

 <asp:GridView ID="gvUnusedAccessories" runat="server">
    <Columns>
        <asp:CommandField ShowSelectButton="True" />
        <asp:TemplateField HeaderText="Select">
            <ItemTemplate >
                <asp:CheckBox ID="chkSelect" runat="server" AutoPostBack="True"/>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:BoundField DataField="Item_Id" HeaderText="ID" ReadOnly="True"/>
        <asp:BoundField DataField="Item_Name" HeaderText="Name" ReadOnly="True"/>  
        <asp:BoundField DataField="AccessoryModel" HeaderText="Modèle" ReadOnly="True"/>
        <asp:BoundField DataField="AccessoryBrand" HeaderText="Marque" ReadOnly="True"/>
    </Columns>
</asp:GridView>

Any hint on how to access the Object contained inside a Row? I know I could actually get the ID and then do a SQL request to my DB, but it seems to be a bit heavy and there must be a better solution.