ASP.NET

public partial class Default : System.Web.UI.Page<br />
{<br />
    protected void Page_PreInit()<br />
    {<br />
        if(IsPostBack)<br />
        {<br />
            this.MasterPageFile = "MasterPage2.master";<br />
        }<br />
    }<br />
    protected void Page_Load(object sender, EventArgs e)<br />
    {<br />
<br />
    }<br />
    protected void Button1_Click(object sender, EventArgs e)<br />
    {<br />
        //Call some event to cause page reload<br />
    }<br />
}