The result

Don’t do it again

One could start to use a long list inside an xsl:choose to fetch each extension… But why do a file-extension mapping again when this is already specified in DOCICON.XML?

Give me my icon

1. Create your ContentByQueryWebPart (CQWP) and export it.
2. Export the webpart
3. Locate the CommonViewFields-property and change it from

   <property name="CommonViewFields" type="string" />

   to

   <property name="CommonViewFields" type="string">HTML_x0020_File_x0020_Type,Text;File_x0020_Type,Text</property>

4. Edit the ItemStyle.xsl or even better create your own My_ItemsStyle.xsl and create a custom template which uses these new ViewFields.

   <xsl:template name="TitleOnlyWithIcon" match="Row[@Style='TitleOnlyWithIcon']" mode="itemstyle">
       <xsl:variable name="SafeLinkUrl">
           <xsl:call-template name="OuterTemplate.GetSafeLink">
               <xsl:with-param name="UrlColumnName" select="'LinkUrl'"/>
           </xsl:call-template>
       </xsl:variable>
       <xsl:variable name="DisplayTitle">
           <xsl:call-template name="OuterTemplate.GetTitle">
               <xsl:with-param name="Title" select="@Title"/>
               <xsl:with-param name="UrlColumnName" select="'LinkUrl'"/>
           </xsl:call-template>
       </xsl:variable>
       <xsl:variable name="LinkTarget">
           <xsl:if test="@OpenInNewWindow = 'True'" >_blank</xsl:if>
       </xsl:variable>
       <div class="item link-item">
           <!-- Here comes the icon -->
           <span class="icon">
               <img src="/_layouts/images/{ddwrt:MapToIcon(string(@HTML_x005F_x0020_File_x005F_x0020_Type),string(@File_x005F_x0020_Type))}" alt="{@DocIcon}" style="vertical-align: middle;margin-right:4px" />
           </span>
           <a href="{$SafeLinkUrl}" target="{$LinkTarget}" title="{@LinkToolTip}">
               <xsl:value-of select="$DisplayTitle"/>
           </a>
       </div>
   </xsl:template>

5. Change the ItemStyle-property inside the webpart-definition to match your custom template. (TitleOnlyWithIcon in this case).
6. Import the webpart

Again there is some magic

If you refresh your page I’m sure you get an error. The magic here is to tell the xsl-stylesheet where to find the MapToIcon-function which resides inside the ddwrt-namespace.

xmlns:ddwrt="http://schemas.microsoft.com/WebParts/v2/DataView/runtime"

The MapToIcon-function does the mapping of the icon by taking the mapping-information from the DOCICON.xml. So even if your icon is not named like the SharePoint ones the icon will be found. My icon here was named icon-pdf.gif for the pdf-file.

Conclusion

The use of the MapToIcon-function is the best method to get the icons. No need for custom “xsl:choose-statements” or “/_layouts/images/ic{@DocIcon}.gif-hacks”.

Object reference not set to an instance of an object

Why?

The CmsDataFormWebpart.MakeSiteRelativeUrl (which is called somewhere when setting this property) needs the HttpContext.Current which isn’t available when using a console application or inside an event receiver (déjà vu!).

Solution

Inside the MSDN-Forums a user named AlexUC found a good workaround.

if (null == HttpContext.Current)
{
    HttpRequest request = new HttpRequest ("", web.Url, "");
    HttpContext.Current = new HttpContext (request, new HttpResponse (new StringWriter ()));
    HttpContext.Current.Items["HttpHandlerSPWeb"] = web;
}

Perhaps this even works when one is inside an asynchronous-event inside an event receiver?! Perhaps one can redirect the user inside the ItemAdded-Method?!
I will analyze this soon….