ASP.NET

[ParseChildren(true), PersistChildren(false)]
[ToolboxData("<{0}:TabStrip runat=server></{0}:TabStrip>")]
public class TabStrip : CompositeControl, IPostBackEventHandler
{
    private Tab mySelectedTab;
    private TabCollection myTabs;

    public TabStrip()
    {
        this.myTabs = new TabCollection(this);
    }

    [MergableProperty(false)]
    public Tab SelectedTab
    {
        get
        {
            foreach (Tab tab in this.Tabs)
                if (tab.IsSelected)
                    return tab;
            return null;
        }
        set { value.IsSelected = true; }
    }

    [PersistenceMode(PersistenceMode.InnerProperty), NotifyParentProperty(true)]
    [MergableProperty(false)]
    public TabCollection Tabs
    {
        get { return myTabs; }
    }
}

<%@ Control Language="C#" AutoEventWireup="true" CodeFile="FileControl.ascx.cs" Inherits="Administration_Controls_FileControl"  %>
<div style="width: 100%; height: 50px;">
    <asp:FileUpload ID="FileUpload1" runat="server" />
    <asp:Button ID="test" runat="server" OnClick="test_click" />
</div>

protected void test_click(object sender, EventArgs e)
{
    if (FileUpload1.HasFile)
    {

    }
}