ASP.NET

public partial class ParentControl : System.Web.UI.UserControl<br />
{<br />
    protected void Page_Load(object sender, EventArgs e)<br />
    {<br />
        if (ViewState["SelectedControl"] != null)<br />
        {<br />
            switch (ViewState["SelectedControl"].ToString())<br />
            {<br />
                case "Control1":<br />
                    PlaceHolder1.Controls.Add(LoadControl("ChildControl.ascx"));<br />
                    break;<br />
                case "Control2":<br />
                    PlaceHolder1.Controls.Add(LoadControl("ChildControl2.ascx"));<br />
                    break;<br />
            }<br />
        }<br />
    }<br />
    protected void LinkButton1_Click(object sender, EventArgs e)<br />
    {<br />
        Control ctrl = LoadControl("ChildControl.ascx");<br />
        PlaceHolder1.Controls.Clear();<br />
        PlaceHolder1.Controls.Add(ctrl);<br />
        ViewState["SelectedControl"] = "Control1";<br />
    }<br />
    protected void LinkButton2_Click(object sender, EventArgs e)<br />
    {<br />
        Control ctrl = LoadControl("ChildControl2.ascx");<br />
        PlaceHolder1.Controls.Clear();<br />
        PlaceHolder1.Controls.Add(ctrl);<br />
        ViewState["SelectedControl"] = "Control2";<br />
    }<br />
}