Introduction
Over the past few months I have been working on branding the
SharePoint portal of one of the largest international companies. This was
really interesting especially that this was the first branding experience for
me. While I was looking at the OOB master page ( default.master
), I noticed there is a control called “delegate control” in the head element
right below the “PlaceHolderAdditionalPageHead”. After googling and
investigating, I can say that Delegate Control is one of the most important
features of SharePoint 2007 when it comes to branding and customization.
History
Back to 2003, When Microsoft released Microsoft SharePoint portal
server 2003, it was cool but what extremely annoyed the developers then is the
non-extensibility of the product and the difficulty of customization.
Now, MOSS 2007 offers many extension points to alter sites even
after they have been provisioned. The introduction of SharePoint features has
opened up an entire world to modifying master pages, page layouts and the pages
themselves. Further, SharePoint introduced Delegate Controls that allow for
more granular control over parts of the page.
Why are they cool and handy ?
On every SharePoint deployment I have ever participated in,
it has been requested that the Search Box be modified. In previous SharePoint
versions, this involved either unghosting and customization and/or creating a
whole new site definition. NOW, Thanks to Delegate Controls, you can take any
control and place them on a SharePoint page such that they substitute the
existing control at whatever scope you desire and yet require no extra coding
or redeployment of the pages themselves. They work hand-in-hand with the newly
introduced Features Framework to dynamically load a control at runtime based on
a key value and sequence number
Enough Theory, How do they work ?
The default.master file that the global site definition
deploys contains some Delegate Controls with the following Id values :
- AdditionalPageHead
- GlobalSiteLink0
- SmallSearchInputBox
- PublishingConsole
For instance, SmallSearchBox displays a search area and the DelegateControl
Definition in default.master is :
<SharePoint:DelegateControl runat=”server” ControlId=” SmallSearchBox”>
All versions of SharePoint contain a feature called ContentLightUp
that includes a Control element that specifies a control for the DelegateControl
with the SmallSearchArea ControlId value. The element looks like this :
<Control Id=”SmallSearchInputBox” Sequence=”100” ControlSrc=”~/_controltempaltes/searcharea.ascx”
/>
The enterprise version of MOSS contains a feature named OSearchEnhancedFeature
that substitutes the searcharea.ascx user control with SearchBoxEx web control
that sends the user to the more advanced search page in MOSS.
<Control Id="SmallSearchInputBox" Sequence="50" ControlClass="Microsoft.SharePoint.Portal.WebControls.SearchBoxEx" ControlAssembly="Microsoft.SharePoint.Portal, Version=12.0.0.0, Culture=neutral,PublicKeyToken=71e9bce111e9429c">
When SharePoint selects the
control to replace the delegate control, it looks through the list of activated
controls and selects the best control and the best control is defined as the
one that has the lowest sequence number. Because the control element in OSearchEnhancedFeature
has a lower sequence number, the control it defines is loaded instead of the
one determined in ContentLightup and this occurs without modifying default.master
.
There are other DelegateControls,
like AdditionalPageHead, that do not have visual elements but instead provide
the ability to insert additional HTML at runtime.
For example, I once created a web
control called SearchEngineOptimizer that emited META tags ( Meta Tags are html tags
that appear in the head of html pages) for search engine optimization and
created a feature to load that web control!
Well, there is a couple of tips and recommendations
that I want to highlight :
- By using a feature scoped at web, you
can use different search boxes for different areas in your site collection
with no extra code.
- You can load user or server controls,
if you are specifying a user control, use URL attribute, if you want to
load a server control use ControlClass and ControlAssembly attributes.
- By adding AllowMultiple=true in to the
delegate control declaration, you can make it load more than one
user/server controls. ( for instance AdditionalPageHead delegate control
is set to allow multiple controls by default).
- When designing your page, create
delegate controls for functionality that might change over time.
- Keep tack of the sequence and don’t
use too low numbers. You don’t want to have trouble overriding the feature
in the future.
Summary
Delegate Controls are important design options for creating
solutions that can mixed and matched with other options. The ability to light
up functionality for one site and not another can be a very important tool in
the SharePoint developer’s toolbox.
