[ToolboxItemAttribute(false)]
public class DemoWebPart : System.Web.UI.WebControls.WebParts.WebPart
{
        [WebBrowsable(false), Personalizable(PersonalizationScope.Shared)]
        public List<string> RootWebs { get; set; }

        [WebBrowsable(false), Personalizable(PersonalizationScope.Shared)]
        public List<string> Webs { get; set; }

        public override EditorPartCollection CreateEditorParts()
        {
            var editor = new DemoEditorpart
                             {
                                 ID = ID + "_Editor",
                                 Title = "Demo Editor Part"
                             };
            return new EditorPartCollection(new EditorPart[] { editor });
        }
}

public class DemoEditorpart : EditorPart
{
    // list box to select site collection's root webs from
    protected ListBox Sites;
    // list box to select webs from
    protected ListBox Webs;

    protected override void CreateChildControls()
    {
        // autopostback
        Sites = new ListBox
                    {
                        CssClass = "UserInput",
                        Width = 176,
                        ID = ID + "Sites",
                        SelectionMode = ListSelectionMode.Multiple,
                        AutoPostBack = true
                    };
        Webs = new ListBox
                   {
                       CssClass = "UserInput",
                       Width = 176,
                       ID = ID + "Webs",
                       SelectionMode = ListSelectionMode.Multiple
                   };

        // get web applications site collection root webs to display
        var sites = GetRootWebs();
        if (sites != null)
        {
            Sites.DataSource = sites;
            Sites.DataTextField = "Title";
            Sites.DataValueField = "Url";
            Sites.Rows = sites.Count + 2;
            Sites.DataBind();
            Sites.SelectedIndexChanged += Sites_SelectedIndexChanged;
        }
        var panel = new UpdatePanel { ID = ID + "UpdatePanel" };
        panel.ContentTemplateContainer.Controls.Add(
            new LiteralControl(@"<table cellspacing=""0"" border=""0""
                    style=""border-width:0px;width:100%;
                    border-collapse:collapse;""><tr><td>
                    <div class=""UserSectionHead"">"));

        panel.ContentTemplateContainer.Controls.Add(
            new LiteralControl(@"Site Collections:<br/>"));
        panel.ContentTemplateContainer.Controls.Add(Sites);
        panel.ContentTemplateContainer.Controls.Add(
            new LiteralControl(@"</div></td></tr>
                    <tr><td>
                    <div style=""width:100%"" class=""UserDottedLine"">
                    </div></td></tr><tr><td>
                    <div class=""UserSectionHead"">"));

        panel.ContentTemplateContainer.Controls.Add(
            new LiteralControl("Sites:<br/>"));
        panel.ContentTemplateContainer.Controls.Add(Webs);
        panel.ContentTemplateContainer.Controls.Add(
            new LiteralControl(@"</div></td></tr><tr><td>
                <div style=""width:100%"" class=""UserDottedLine""></div>
                </td></tr></table>"));

        Controls.Add(panel);
        base.CreateChildControls();

    }

    /// <summary>
    /// event handler to list webs under the selected site collection
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    protected void Sites_SelectedIndexChanged(object sender, EventArgs e)
    {
        FillWebs(Sites.Items, Webs.Items);
        Webs.Rows = Webs.Items.Count + 2;
    }

    /// <summary>
    /// fill the Webs list box according to the selected site collection
    /// </summary>
    /// <param name="sites">site collections</param>
    /// <param name="webs">webs</param>
    private static void FillWebs(ListItemCollection sites,
        ListItemCollection webs)
    {
        foreach (ListItem item in sites)
        {
            var newsWebs = GetWebs(item.Value);
            foreach (var web in newsWebs)
            {
                var listItem = new
                    ListItem(web.Title,
                    item.Value + ";" + web.ServerRelativeUrl);
                if (item.Selected && !webs.Contains(listItem))
                {
                    webs.Add(listItem);
                }
                else if (!item.Selected && webs.Contains(listItem))
                {
                    webs.Remove(listItem);
                }
            }
        }
    }

    /// <summary>
    /// apply changes to web part
    /// </summary>
    /// <returns></returns>
    public override bool ApplyChanges()
    {
        var part = (DemoWebPart)WebPartToEdit;
        // apply values back to web part from editor part
        part.RootWebs = ApplyRootWebs(Sites.Items);
        part.Webs = ApplyWebs(Webs.Items);
        return true;
    }

    /// <summary>
    /// sync changes from web part
    /// </summary>
    public override void SyncChanges()
    {
        EnsureChildControls();
        var part = (DemoWebPart)WebPartToEdit;
        // sync values from web part to editor part
        SyncRootWebs(Sites.Items, part.RootWebs);
        SyncWebs(Sites.Items, Webs.Items, part.Webs);
        Webs.Rows = Webs.Items.Count + 2;
    }

    /// <summary>
    /// apply selected site collections to web part
    /// </summary>
    /// <param name="listItems">Sites items</param>
    /// <returns>list of selected site collections</returns>
    private static List<string> ApplyRootWebs(IEnumerable listItems)
    {
        return (from ListItem listItem in listItems
                where listItem.Selected
                select string.Format("{0};{1};{2}", listItem.Text,
                listItem.Value, string.Empty)).ToList();
    }

    /// <summary>
    /// apply selected webs to web part
    /// </summary>
    /// <param name="listItems">Webs items</param>
    /// <returns>list of seleted webs</returns>
    private static List<string> ApplyWebs(IEnumerable listItems)
    {
        return (from ListItem listItem in listItems
                where listItem.Selected
                select string.Format("{0};{1};{2}", listItem.Text,
                listItem.Value.Split(';')[0],
                listItem.Value.Split(';')[1])).ToList();
    }

    /// <summary>
    /// sync site collections from web part
    /// </summary>
    /// <param name="rootWebItems">Sites items</param>
    /// <param name="rootWebs">selecetd site collections from web part</param>
    private static void SyncRootWebs(ListItemCollection rootWebItems,
        IEnumerable<string> rootWebs)
    {
        if (rootWebs == null) return;

        foreach (var siteInfo in rootWebs.Select(rootWeb =>
            rootWeb.Split(';')))
        {
            var rootWebItem = rootWebItems.FindByValue(siteInfo[1]);
            if (rootWebItem != null) rootWebItem.Selected = true;
        }
    }

    /// <summary>
    /// sync webs from web part
    /// </summary>
    /// <param name="rootWebItems">Sites items</param>
    /// <param name="webItems">Webs items</param>
    /// <param name="webs">selected webs from web part</param>
    private static void SyncWebs(ListItemCollection rootWebItems,
        ListItemCollection webItems,
        IEnumerable<string> webs)
    {
        if (webs == null) return;

        FillWebs(rootWebItems, webItems);

        foreach (var siteInfo in webs.Select(web => web.Split(';')))
        {
            var webItemValue = string.Format("{0};{1}", siteInfo[1],
                siteInfo[2]);
            var webItem = webItems.FindByValue(webItemValue);
            if (webItem != null) webItem.Selected = true;
        }
    }

    /// <summary>
    /// get every root web from web application - display also the
    /// names of those site collections user has no right to
    /// </summary>
    /// <returns>list of webs</returns>
    private static List<SPWeb> GetRootWebs()
    {
        var webs = new List<SPWeb>();

        SPSecurity.RunWithElevatedPrivileges(delegate
        {
            foreach (SPSite site in
                  SPContext.Current.Site.WebApplication.Sites)
            {
                webs.Add(site.RootWeb);
            }
        });

        return webs;
    }

    /// <summary>
    /// get sub webs published with a certain template
    /// </summary>
    /// <param name="siteName">site name</param>
    /// <returns>list of webs</returns>
    private static List<SPWeb> GetWebs(string siteName)
    {
        SPSite site = null;
        SPSecurity.RunWithElevatedPrivileges(delegate
        {
            site = SPContext.Current.Site.WebApplication.Sites[siteName];
        });
        return GetWebs(site ?? SPContext.Current.Site);
    }

    /// <summary>
    /// get sub webs published with a certain template
    /// </summary>
    /// <param name="site">site</param>
    /// <returns>list of webs</returns>
    private static List<SPWeb> GetWebs(SPSite site)
    {
        return site.RootWeb.GetSubwebsForCurrentUser().Where(w =>
            w.WebTemplate.Equals("MyCustomSiteTemplate",
            StringComparison.OrdinalIgnoreCase)).ToList();
    }
}