Add MasterPage Dynamically from CodeBehind asp.net c#

protected void Page_PreInit(object sender, EventArgs e)
{
string masterPath = string.Empty;
string _userType = Request.QueryString[“sType”].ToString();
switch (_userType)
{
case “User”:
masterPath = “~/User/Master/”;
Page.MasterPageFile = masterPath + “UserMaster.master”;
break;
case “Admin”:
masterPath = “~/Admin/Master/”;
Page.MasterPageFile = masterPath + “AdminMaster.master”;
break;
default:
Page.MasterPageFile = masterPath + “MainMaster.master”;
break;
}
}