属性窗格中未显示Webpart属性

Question

刚刚为SharePoint创建了一个简单的Visual WebPart。还没有代码。我想要的只是“Whatever”-Property显示在该webpart的Propertypane中。但事实并非如此。

（甚至没有显示类别）

我在这里做错了什么？

using System;
using System.ComponentModel;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using Microsoft.SharePoint;
using Microsoft.SharePoint.WebControls;
using Microsoft.SharePoint.WebPartPages;
using WebPart = System.Web.UI.WebControls.WebParts.WebPart;

namespace tqUpdateOrder.ListOrder
{
    [ToolboxItemAttribute(false)]
    public class ListOrder : WebPart
    {
        // Visual Studio might automatically update this path when you change the Visual Web Part project item.
        private const string _ascxPath = @"~/_CONTROLTEMPLATES/15/tqUpdateOrder/ListOrder/ListOrderUserControl.ascx";

        private string _whatever;

        [Browsable(true),FriendlyName("oink"),WebBrowsable(true),WebDisplayName("OINK OINK"),Category("HIER BIN ICH")]

        public string Whatever
        {
            get { return _whatever; }
            set { _whatever = value; }
        }

        protected override void CreateChildControls()
        {
            Control control = Page.LoadControl(_ascxPath);
            Controls.Add(control);
        }
    }
}