Show Popup Message in C#.Net

Show Popup Message in C#.Net

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
using System.Text;
public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        ShowPopUpMsg ("This is popup message.");
    }
    private void ShowPopUpMsg(string msg)
    {
        System.Text.StringBuilder sb = new System.Text.StringBuilder();
        sb.Append("alert('");
        sb.Append(msg.Replace("\n", "\\n").Replace("\r", "").Replace("'", "\\'"));
        sb.Append("');");
        ScriptManager.RegisterStartupScript(this.Page, this.GetType(), "showalert", sb.ToString(), true);
    }
}