Show JavaScript alert based on CheckBox selection in ASP.Net GridView on Button Click using C# and VB.Net

I am checking it, Will get back to you soon.

Hi narasiman,

Please refer below sample.

HTML

<asp:GridView ID="gvCustomers" runat="server" AutoGenerateColumns="false">
    <Columns>
        <asp:TemplateField>
            <ItemTemplate>
                <asp:CheckBox ID="chk" runat="server" />
            </ItemTemplate>
        </asp:TemplateField>
        <asp:BoundField DataField="CustomerId" HeaderText="CustomerId" />
        <asp:BoundField DataField="Name" HeaderText="Name" />
        <asp:BoundField DataField="Country" HeaderText="Country" />
    </Columns>
</asp:GridView>
<asp:Button Text="Submit" runat="server" OnClick="Select" />

Namespaces

C#

using System.Data;
using System.Data.SqlClient;
using System.Configuration;

VB.Net

Imports System.Data
Imports System.Data.SqlClient
Imports System.Configuration

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        gvCustomers.DataSource = GetData();
        gvCustomers.DataBind();
    }
}

private DataTable GetData()
{
    using (SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["constr"].ConnectionString))
    {
        using (SqlCommand cmd = new SqlCommand("SELECT * FROM Customers", con))
        {
            using (SqlDataAdapter da = new SqlDataAdapter(cmd))
            {
                DataTable dt = new DataTable();
                da.Fill(dt);
                return dt;
            }
        }
    }
}

protected void Select(object sender, EventArgs e)
{
    DataTable dt = GetData();
    for (int i = 0; i < gvCustomers.Rows.Count; i++)
    {
        CheckBox checkbox = (CheckBox)gvCustomers.Rows[i].Cells[0].FindControl("chk");
        if (checkbox.Checked)
        {
            if (dt.Select("Name='" + gvCustomers.Rows[i].Cells[2].Text + "'").Length > 1)
            {
                ScriptManager.RegisterStartupScript(this, this.GetType(), "CropImage", "alert('" + gvCustomers.Rows[i].Cells[2].Text + " is duplicate.')", true);
                break;
            }
        }
    }
}

VB.Net

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
        If Not Me.IsPostBack Then
            gvCustomers.DataSource = GetData()
            gvCustomers.DataBind()
        End If
    End Sub

    Private Function GetData() As DataTable
        Using con As SqlConnection = New SqlConnection(ConfigurationManager.ConnectionStrings("constr").ConnectionString)

            Using cmd As SqlCommand = New SqlCommand("SELECT * FROM Customers", con)

                Using da As SqlDataAdapter = New SqlDataAdapter(cmd)
                    Dim dt As DataTable = New DataTable()
                    da.Fill(dt)
                    Return dt
                End Using
            End Using
        End Using
    End Function

    Protected Sub [Select](ByVal sender As Object, ByVal e As EventArgs)
        Dim dt As DataTable = GetData()

        For i As Integer = 0 To gvCustomers.Rows.Count - 1
            Dim checkbox As CheckBox = CType(gvCustomers.Rows(i).Cells(0).FindControl("chk"), CheckBox)

            If checkbox.Checked Then

                If dt.[Select]("Name='" & gvCustomers.Rows(i).Cells(2).Text & "'").Length > 1 Then
                    ScriptManager.RegisterStartupScript(Me, Me.[GetType](), "CropImage", "alert('" & gvCustomers.Rows(i).Cells(2).Text & " is duplicate.')", True)
                    Exit For
                End If
            End If
        Next
    End Sub

Screenshot