I have to display an alert on Android mobile phone. I'm working with asp.net (c#) and when I use:
protected void CheckNumber(object sender, EventArgs e)
{
    ...
    if (Convert.ToInt64(TextBox.Text) <= 0)
    {
         Response.Write("<script>alert('The number must be positive')</script>");
         return;
    }
    ...
}
there is no message or screen which opens on top.
I have also tried this without any difference:
if (Convert.ToInt64(TextBox.Text) <= 0)
{
      MessageBox.Show("The number must be positive!");
      return;
}
...
How can I have a message and a confirm button on the mobile screen?
 
    