How to get value of GridView BoundField set to Visible = False in ASP.Net

If you have set the dataKeyNames in the GridView  And you have set the BoundField column to visible false the you need to find the DataKey value of each row to delete.

foreach (GridViewRow row in this.GridView1.Rows)
{
    int id = Convert.ToInt32(this.GridView1.DataKeys[row.RowIndex].Value);
}

Complete Example

HTML

<asp:GridView ID="GridView1" HeaderStyle-BackColor="#3AC0F2" DataKeyNames="Id" HeaderStyle-ForeColor="White"
    runat="server" AutoGenerateColumns="false">
    <Columns>
        <asp:BoundField DataField="Id" HeaderText="Id" ItemStyle-Width="30" Visible="false" />
        <asp:BoundField DataField="Name" HeaderText="Name" ItemStyle-Width="150" />
        <asp:BoundField DataField="Country" HeaderText="Country" ItemStyle-Width="150" />
    </Columns>
</asp:GridView>
<asp:Button Text="Delete All Rows" OnClick="DeleteAll" runat="server" />

Namespace

using System.Data;

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[3] { new DataColumn("Id", typeof(int)),
                        new DataColumn("Name", typeof(string)),
                        new DataColumn("Country",typeof(string)) });
        dt.Rows.Add(1, "John Hammond", "United States");
        dt.Rows.Add(2, "Mudassar Khan", "India");
        dt.Rows.Add(3, "Suzanne Mathews", "France");
        dt.Rows.Add(4, "Robert Schidner", "Russia");
        GridView1.DataSource = dt;
        GridView1.DataBind();
    }
}
// You need to write the Delete code inside foreach loop
protected void DeleteAll(object sender, EventArgs e)
{
    foreach (GridViewRow row in this.GridView1.Rows)
    {
        int id = Convert.ToInt32(this.GridView1.DataKeys[row.RowIndex].Value);
    }
}