在第一部分中实现的将附件显示成图片的方式,只能是在列表所在的站点中,跨站(Cross-site)的时候就不能显示了.我经过很长时间的尝试后发现,AttachmentField在跨转的时候,其内部的ItemContext只能是当前访问站点的Context,所以会在当前站点下去查找相应的List与Field,这导致了根本就找不到,所以也就什么也显示不出来了.

       在确定了不可能使用AttachmentField进行跨站显示附件后,我重新写了一个控件来模拟生成与AttachmentField一模一样的输出.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Web.UI;
using System.Web.UI.WebControls;
using Microsoft.SharePoint;
using System.Web.UI.HtmlControls;
using Microsoft.SharePoint.Security;
using System.Web;
using System.Security.Permissions;

namespace Only.SPLibraryExtend.WebControls
{
    /// <summary>
    /// 用来显示附件列表 完全模拟SharePoint的AttachmentField的输出
    /// </summary>
    [SharePointPermission(SecurityAction.InheritanceDemand, ObjectModel = true), AspNetHostingPermission(SecurityAction.InheritanceDemand, Level = AspNetHostingPermissionLevel.Minimal), SharePointPermission(SecurityAction.LinkDemand, ObjectModel = true), AspNetHostingPermission(SecurityAction.LinkDemand, Level = AspNetHostingPermissionLevel.Minimal)]
    public class AttachmentsField:Control
    {
        public int ItemId
        {
            get;
            set;
        }

        public string ListName
        {
            get;
            set;
        }

        public string WebUrl
        {
            get;
            set;
        }

        protected override void CreateChildControls()
        {
            base.CreateChildControls();

            SPSite site = SPContext.Current.Web.Site;

            using (SPWeb web = site.OpenWeb(WebUrl))
            {
                SPList list = web.Lists[ListName];
                SPListItem item = list.GetItemById(ItemId);
                HtmlTable table = new HtmlTable();
                table.Attributes["id"]="idAttachmentsTable";                
                table.Border = 0;
                table.CellSpacing = 0;
                table.CellPadding = 0;
                foreach (String attachmentname in item.Attachments)
                {
                    String attachmentAbsoluteURL = item.Attachments.UrlPrefix + attachmentname;
                    HtmlTableRow tr = new HtmlTableRow();
                    tr.Attributes["id"]=Guid.NewGuid().ToString();                    

                    HtmlTableCell cell = new HtmlTableCell();
                    cell.Attributes["class"] = "ms-vb";
                    
                    HtmlGenericControl span=new HtmlGenericControl("Span");
                    span.Attributes["dir"]="ltr";
                    
                    HtmlGenericControl A=new HtmlGenericControl("a");
                    A.Attributes["tabIndex"] = "1";
                    A.Attributes["onmousedown"] = @"return VerifyHref(this, event, '0', 'SharePoint.OpenDocuments.3', '');return false;";
                    A.Attributes["onclick"] =@"DispDocItemExWithServerRedirect(this, event, 'FALSE', 'FALSE', 'FALSE', 'SharePoint.OpenDocuments.3', '0', '');return false;";
                    A.Attributes["href"] = attachmentAbsoluteURL;
                    A.InnerText = attachmentname;

                    span.Controls.Add(A);
                    cell.Controls.Add(span);
                    LiteralControl nbsp = new LiteralControl("&nbsp;&nbsp;&nbsp;&nbsp;");
                    cell.Controls.Add(nbsp);                    

                    tr.Cells.Add(cell);

                    table.Rows.Add(tr);
                }
                this.Controls.Add(table);
            }                        
        }
    }
}

这个控件需要配置ItemId,WebUrl以及ListName,以便能够找到相应的Item.这三个属性在配置DataFormWebPart进行跨转显示数据的属性是一样的,当然这三个属性在DataFormWebPart进行跨站时是配置在SPDataSource对象的参数上的.要将这个控件嵌入到DataFormWebPart中,需要

【原创】如何在DataFormWebPart中嵌入自定义控件[How to embeded custom control in DFWP]这篇文章中的相应内容,所以在DataFormWebPart中加入

<xsl:element name="Only:AttachmentsField">
    <xsl:attribute name="runat">server</xsl:attribute>
    <xsl:attribute name="ListName">园区企业</xsl:attribute>
    <xsl:attribute name="WebUrl">/admin</xsl:attribute>
    <xsl:attribute name="ItemId"><xsl:value-of select="@ID" /></xsl:attribute>
</xsl:element>

在配合了相应的CSS的的最终显示效果是