Check (Validate) if record exists in GridView when adding new row in ASP.Net

Here I have created sample for you that checks before inserting data. Here I have checked Name before Inserting.

HTML

<asp:GridView ID="GridView1" runat="server" CssClass="Grid" AutoGenerateColumns="false"
    EmptyDataText="No records has been added.">
    <Columns>
        <asp:BoundField DataField="Name" HeaderText="Name" ItemStyle-Width="120" />
        <asp:BoundField DataField="Country" HeaderText="Country" ItemStyle-Width="120" />
    </Columns>
</asp:GridView>
<br />
<table border="0" cellpadding="0" cellspacing="0" style="border-collapse: collapse">
    <tr>
        <td style="padding-bottom: 10px">
            Name:<br />
            <asp:TextBox ID="txtName" runat="server" />
        </td>
    </tr>
    <tr>
        <td style="padding-bottom: 10px">
            Country:<br />
            <asp:TextBox ID="txtCountry" runat="server" />
        </td>
    </tr>
    <tr>
        <td style="width: 100px">
            <asp:Button ID="btnAdd" runat="server" Text="Add" OnClick="Insert" />
        </td>
    </tr>
    <tr>
        <td>
            <asp:Label ID="lblErrorMessage" Text="Name Already Exists" runat="server" Visible="false" />
        </td>
    </tr>
</table>

Namespace

using System.Data;

Code

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[2] { new DataColumn("Name"), new DataColumn("Country") });
        ViewState["Customers"] = dt;
        this.BindGrid();
    }
}

protected void BindGrid()
{
    GridView1.DataSource = (DataTable)ViewState["Customers"];
    GridView1.DataBind();
}

protected void Insert(object sender, EventArgs e)
{
    DataTable dt = (DataTable)ViewState["Customers"];
    bool ifExist = false;
    foreach (DataRow dr in dt.Rows)
    {
        if (dr["Name"].ToString() == txtName.Text.Trim())
        {
            ifExist = true;
        }
    }
    if (!ifExist)
    {
        dt.Rows.Add(txtName.Text.Trim(), txtCountry.Text.Trim());
        ViewState["Customers"] = dt;
        this.BindGrid();
        txtName.Text = string.Empty;
        txtCountry.Text = string.Empty;
    }
    else
    {
        this.lblErrorMessage.Visible = true;
    }
}

Screenshot