webaprt在SPD设计视图下呈现

1.webpart需要继承接口Microsoft.SharePoint.WebControls.IDesignTimeHtmlProvider，实现GetDesignTimeHtml();

2.wbpart继承System.Web.UI.Design. HtmlControlDesigner,重写GetDesignTimeHtml();

3.在protected override void RenderContents(HtmlTextWriter writer)中

if (this.DesignMode)
{
    ......
    return;
}