SharePoint provides a mechanism that allows developers to customize out-of-the-box functionality in pages, without the need for modifying the pages that come with SharePoint. This mechanism is provided with delegate controls. I am going to show you how to create a delegate control that you can use to override the Global Navigation bar at the top of standard SharePoint pages.
Definition
First off, it's important to understand what a delegate control is, so we can properly create and apply it in the specific situation we are developing for. A delegate control defines a region in an aspx page that allows the content to be replaced with our custom content. This custom content is created via a SharePoint feature, and when deployed and activated, replaces the standard content at runtime.
Development
The Global Navigation bar is located at the top of all the pages in a site, and the master page uses a delegate control in a placeholder to determine what to render at runtime. Here is the markup for the delegate control:
<SharePoint:DelegateControl runat="server" ControlId="GlobalNavigation"/>
Note that the ControlId value determines what delegate control is, so for our example the Global Navigation bar has a ControlId value of GlobalNavigation.
Once we know the name of the delegate control we are working with, we are ready to write code for our delegate control.
Open Visual Studio 2010 and create a new Empty SharePoint project. Map a folder to the CONTROLTEMPLATES directory in the SharePoint root (the 14 hive). Add a new SharePoint 2010 User Control by right-mouse clicking the CONTROLTEMPLATES mapped directory, from the Solution Explorer. Give the user control an appropriate name (I named it ucGlobNavDelegateControl). Once the control is created, open it in the Designer and add some markup:
You will also need to create an Elements.xml file, so add a module to the project, which will create the Elements.xml file as part of it (you can delete the Sample.txt file created).
Delete the markup between the Elements tags, and add the following markup:
<Control Id = "GlobalNavigation" Sequence="90" ControlSrc="~/_ControlTemplates/ucGlobNavDelegateControl.ascx" />
This markup associates the delegate control we are creating with the delegate control placeholder defined in the master pages in a SharePoint site collection. Note that the ControlId value equals GlobalNavigation, which specifies that our custom delegate control is overriding the Global Navigation control. The Sequence value must be less than 100, since SharePoint will render the control with the lowest sequence (the default control is set at 100). The ControlSrc value indicates the location to our custom delegate control.
Deployment
Deploying our custom delegate control is done using a feature, so create a feature in Visual Studio and name it MyCustomGlobalNavigationFeature. Add the module you created to it, and set the feature scope to Web. Compile and deploy the project to your SharePoint site.
Once your feature is deployed successfully, you should be able to verify that your feature has been deployed and activated in your site by managing the Site Features, under Site Settings. Look for your deployed feature, as shown here:
If your feature is properly activated, you should now see the Global Navigation replaced by your custom delegate control:
Conclusion
And that's all there is to it! Of course, the example here is basic, so there is a lot more that can be done with delegate controls. I am also including a screenshot of my Solution Explorer in Visual Studio, so you can get an idea of how my example project was structured:
