Hi rakeshkuma,

Check this example. Now please take its reference and correct your code.

HTML

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false" ShowFooter="true" OnRowEditing="OnRowEditing">
    <Columns>
        <asp:TemplateField HeaderText="Id">
            <ItemTemplate>
                <asp:Label ID="lblId" runat="server" Text='<%# Eval("Id") %>' />
            </ItemTemplate>
            <EditItemTemplate>
                <asp:Label ID="lblId" runat="server" Text='<%# Eval("Id") %>' />
            </EditItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Name">
            <ItemTemplate>
                <asp:Label ID="lblName" runat="server" Text='<%# Eval("Name") %>' />
            </ItemTemplate>
            <EditItemTemplate>
                <asp:TextBox ID="txtName" runat="server" Text='<%# Eval("Name") %>' />
            </EditItemTemplate>
            <FooterTemplate>
                <asp:TextBox ID="txtName" runat="server" Text="" />
            </FooterTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Country">
            <ItemTemplate>
                <asp:Label ID="lblCountry" runat="server" Text='<%# Eval("Country") %>' />
            </ItemTemplate>
            <EditItemTemplate>
                <asp:TextBox ID="txtCountry" runat="server" Text='<%# Eval("Country") %>' />
            </EditItemTemplate>
            <FooterTemplate>
                <asp:TextBox ID="txtCountry" runat="server" Text="" />
            </FooterTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Action">
            <ItemTemplate>
                <asp:LinkButton Text="Edit" runat="server" CommandName="Edit" />
                <asp:LinkButton Text="Delete" runat="server" OnClick="OnDelete" />
            </ItemTemplate>
            <EditItemTemplate>
                <asp:LinkButton Text="Update" runat="server" OnClick="OnUpdate" />
                <asp:LinkButton Text="Cancel" runat="server" OnClick="OnCancel" />
            </EditItemTemplate>
            <FooterTemplate>
                <asp:Button ID="btnAdd" runat="server" Text="Add" OnClick="OnAdd" Width="75px" CommandName="Footer" />
            </FooterTemplate>
        </asp:TemplateField>
    </Columns>
    <EmptyDataTemplate>
        <table>
            <tr>
                <th scope="col">Id</th>
                <th scope="col">Name</th>
                <th scope="col">Country</th>
                <th scope="col">Action</th>
            </tr>
            <tr>
                <td></td>
                <td><asp:TextBox ID="txtName" runat="server" Text="Test Country" /></td>
                <td><asp:TextBox ID="txtCountry" runat="server" Text="Test Country" /></td>
                <td><asp:Button ID="btnAdd" runat="server" Text="Add" OnClick="OnAdd" Width="75px" CommandName="EmptyDataTemplate" /></td>
            </tr>
        </table>
    </EmptyDataTemplate>
</asp:GridView>

Namespaces

C#

using System.Data;

VB.Net

Imports System.Data

Code

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"), new DataColumn("Name"), new DataColumn("Country") });
        dt.Rows.Add(1, "John Hammond", "USA");
        dt.Rows.Add(2, "Mudassar Khan", "India");
        dt.Rows.Add(3, "Suzanne Mathews", "France");
        dt.Rows.Add(4, "Robert Schidner", "UK");
        ViewState["Data"] = dt;

        this.BindGrid();
    }
}

protected void OnAdd(object sender, EventArgs e)
{
    Control control = null;
    if (GridView1.FooterRow != null)
    {
        control = GridView1.FooterRow;
    }
    else
    {
        control = GridView1.Controls[0].Controls[0];
    }
    string name = (control.FindControl("txtName") as TextBox).Text.Trim();
    string country = (control.FindControl("txtCountry") as TextBox).Text.Trim();
    DataTable dt = ViewState["Data"] as DataTable;
    int lastId;
    if (dt.Rows.Count == 0)
    {
        lastId = 1;
        dt.Rows.Add(lastId, name, country);
    }
    else
    {
        lastId = Convert.ToInt32(dt.Rows[dt.Rows.Count - 1]["Id"].ToString());
        dt.Rows.Add(lastId + 1, name, country);
    }
    ViewState["Data"] = dt;
    this.BindGrid();
}

protected void OnDelete(object sender, EventArgs e)
{
    int index = ((sender as LinkButton).NamingContainer as GridViewRow).RowIndex;
    DataTable dt = ViewState["Data"] as DataTable;
    dt.Rows[index].Delete();
    ViewState["Data"] = dt;
    this.BindGrid();
}

protected void OnRowEditing(object sender, GridViewEditEventArgs e)
{
    GridView1.EditIndex = e.NewEditIndex;
    this.BindGrid();
}

protected void OnUpdate(object sender, EventArgs e)
{
    GridViewRow row = (sender as LinkButton).NamingContainer as GridViewRow;
    string name = (row.FindControl("txtName") as TextBox).Text;
    string country = (row.FindControl("txtCountry") as TextBox).Text;
    DataTable dt = ViewState["Data"] as DataTable;
    dt.Rows[row.RowIndex]["Name"] = name;
    dt.Rows[row.RowIndex]["Country"] = country;
    ViewState["Data"] = dt;
    GridView1.EditIndex = -1;
    this.BindGrid();
}

protected void OnCancel(object sender, EventArgs e)
{
    GridView1.EditIndex = -1;
    this.BindGrid();
}

private void BindGrid()
{
    DataTable dt = ViewState["Data"] as DataTable;
    GridView1.DataSource = dt;
    GridView1.DataBind();
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        Dim dt As DataTable = New DataTable()
        dt.Columns.AddRange(New DataColumn(2) {
                            New DataColumn("Id"), New DataColumn("Name"), New DataColumn("Country")})
        dt.Rows.Add(1, "John Hammond", "USA")
        dt.Rows.Add(2, "Mudassar Khan", "India")
        dt.Rows.Add(3, "Suzanne Mathews", "France")
        dt.Rows.Add(4, "Robert Schidner", "UK")
        ViewState("Data") = dt
        Me.BindGrid()
    End If
End Sub

Protected Sub OnAdd(ByVal sender As Object, ByVal e As EventArgs)
    Dim control As Control = Nothing
    If GridView1.FooterRow IsNot Nothing Then
        control = GridView1.FooterRow
    Else
        control = GridView1.Controls(0).Controls(0)
    End If
    Dim name As String = (TryCast(control.FindControl("txtName"), TextBox)).Text.Trim()
    Dim country As String = (TryCast(control.FindControl("txtCountry"), TextBox)).Text.Trim()
    Dim dt As DataTable = TryCast(ViewState("Data"), DataTable)
    Dim lastId As Integer
    If dt.Rows.Count = 0 Then
        lastId = 1
        dt.Rows.Add(lastId, name, country)
    Else
        lastId = Convert.ToInt32(dt.Rows(dt.Rows.Count - 1)("Id").ToString())
        dt.Rows.Add(lastId + 1, name, country)
    End If
    ViewState("Data") = dt
    Me.BindGrid()
End Sub

Protected Sub OnDelete(ByVal sender As Object, ByVal e As EventArgs)
    Dim index As Integer = (TryCast((TryCast(sender, LinkButton)).NamingContainer, GridViewRow)).RowIndex
    Dim dt As DataTable = TryCast(ViewState("Data"), DataTable)
    dt.Rows(index).Delete()
    ViewState("Data") = dt
    Me.BindGrid()
End Sub

Protected Sub OnRowEditing(ByVal sender As Object, ByVal e As GridViewEditEventArgs)
    GridView1.EditIndex = e.NewEditIndex
    Me.BindGrid()
End Sub

Protected Sub OnUpdate(ByVal sender As Object, ByVal e As EventArgs)
    Dim row As GridViewRow = TryCast((TryCast(sender, LinkButton)).NamingContainer, GridViewRow)
    Dim name As String = (TryCast(row.FindControl("txtName"), TextBox)).Text
    Dim country As String = (TryCast(row.FindControl("txtCountry"), TextBox)).Text
    Dim dt As DataTable = TryCast(ViewState("Data"), DataTable)
    dt.Rows(row.RowIndex)("Name") = name
    dt.Rows(row.RowIndex)("Country") = country
    ViewState("Data") = dt
    GridView1.EditIndex = -1
    Me.BindGrid()
End Sub

Protected Sub OnCancel(ByVal sender As Object, ByVal e As EventArgs)
    GridView1.EditIndex = -1
    Me.BindGrid()
End Sub

Private Sub BindGrid()
    Dim dt As DataTable = TryCast(ViewState("Data"), DataTable)
    GridView1.DataSource = dt
    GridView1.DataBind()
End Sub

Screenshot