Asp.Net Kontrolleri - Attributes

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        Button1.Attributes.Add("onmouseover", "alert('Buton 1 in üzerine gelindi')");
    }
    else
    {
        Button1.Attributes.Remove("onmouseover");
    }
}