You need to add the Redirection code. I have given you the code for setting the Data in Session and Retrieve it at the Page load.
Add this line in the Button Event at the End of event.
Button Click event
protected void SetView(object sender, EventArgs e)
{
//Set the active view by date
Session["ActiveView"] = 2;
Response.Redirect("~/Default.aspx");
}
Page2 PageLoad
protected void Page_Load(object sender, EventArgs e)
{
if (Session["ActiveView"] != null)
{
this.MultiView1.ActiveViewIndex = Convert.ToInt32(Session["ActiveView"]);
}
}