In this article I will explain with an example, how to get value of a BoundField column in GridView which is set Visible property to False in ASP.Net using C# and VB.Net.
When the Visible property of the BoundField column is set to False, then it is not possible to get value of such column and hence, DataKeyNames (DataKeys) property of ASP.Net GridView will be used.
What are DataKeyNames and DataKeys?
DataKeyNames is the property of GridView which allows us to set the names of the Column Fields, that we want to use in code but do not want to display it. Example Primary Keys, ID fields, etc.
The values Column Fields which are set in DataKeyNames are available in code in DataKeys object which saves it in an Array called as DataKeyArray.
HTML Markup
The following HTML Markup consists of:
GridView - For displaying the records.
The GridView has been assigned with a DataKeyNames property.
The GridView consists of two BoundField columns and one TemplateField column consisting of a Button control.
The Button has been assigned with an OnClick event handler.
<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false" DataKeyNames="Id">
        <asp:BoundField DataField="Name" HeaderText="Name" />
        <asp:BoundField DataField="Country" HeaderText="Country" />
                <asp:Button ID="btnGet" Text="Get Value" runat="server" OnClick="OnGet" />
You will need to import the following namespace.
using System.Data;
Imports System.Data
Binding the GridView
Inside the Page Load event handler, the GridView is populated with data by making use of a dynamic DataTable with some records.
Note: For more details on how to use dynamic DataTable, please refer my article Dynamically create DataTable and bind to GridView in ASP.Net.
protected void Page_Load(object sender, EventArgs e)
    if (!this.IsPostBack)
        DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[3] {
            new DataColumn("Id"),
            new DataColumn("Name"),
            new DataColumn("Country") });
        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;
Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        Dim dt As New DataTable()
        dt.Columns.AddRange(New DataColumn(2) {
                            New DataColumn("Id"),
                            New DataColumn("Name"),
                            New DataColumn("Country")})
        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
    End If
End Sub
Getting the DataKeys value for a particular GridView Row
When Get Value Button is clicked, following event handler is executed.
Inside this event handler, first the GridView Row is determined using the NamingContainer property and then, the Row Index is determined.
Next, using the Row Index, the DataKeys array is accessed and the value of the Column is fetched.
Finally, the DataKey is displayed using JavaScript Alert Message Box.
protected void OnGet(object sender, EventArgs e)
    //Determine the RowIndex of the Row whose Button was clicked.
    int rowIndex = ((sender as Button).NamingContainer as GridViewRow).RowIndex;
    //Get the value of column from the DataKeys using the RowIndex.
    int id = Convert.ToInt32(GridView1.DataKeys[rowIndex].Values[0]);
    ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('DataKey: " + id + "');", true);
Protected Sub OnGet(sender As Object, e As EventArgs)
    'Determine the RowIndex of the Row whose Button was clicked.
    Dim rowIndex As Integer = TryCast(TryCast(sender, Button).NamingContainer, GridViewRow).RowIndex
    'Get the value of column from the DataKeys using the RowIndex.
    Dim id As Integer = Convert.ToInt32(GridView1.DataKeys(rowIndex).Values(0))
    ClientScript.RegisterStartupScript(Me.GetType(), "alert", "alert('DataKey: " & id & "');", True)
End Sub
DataKeyNames in GridView example in ASP.Net