One of the cool new features in the upcoming Summer' 11 release is Dynamic Visualforce Components. Dave Carroll demoed this feature in the Summer' 11 Preview webinar that he and I did a couple of weeks back. You can watch a recording of the full webinar here, but if you just want to see the Dynamic VF components demo, jump to this point of the recording. You can also find detailed documentation for this feature in the VF Developers Guide for Summer' 11 (Note for visitors from the future: 1) who won the 2011 World Series? and b) this documentation link will change once Summer' 11 is GA).
Lets take a look at the sample code demoed during the webinar and dig a little deeper into this feature. Before we get to the code however, lets lay some groundwork.
1) So what are Dynamic Visualforce Components? This is a new VF feature introduced as Pilot in Summer' 11 (i.e. you need to contact Salesforce support to have it enabled in your Org). With this feature, you can generate VF markup in Apex controller/extension code and then insert that markup at runtime in the VF page to generate truly dynamic VF pages whose structure/content is determined at runtime. For example, you can generate an entire <apex:outputPanel> (including all its child elements) in the controller based on some business logic/conditions and then insert that panel into the VF page at runtime.
2) Why the new feature? The Visualforce team has been adding support for dynamic VF content over the last couple of releases. Dynamic VF bindings and Field Sets were the first pieces. Dynamic VF components is the next evolution in that journey and it allows developers and ISVs to generate truly dynamic VF pages.
Lastly, Dynamic VF components allow you to implement functionality that is just not possible with the use of 'rendered' attributes. For example, if the page composition/structure is completely dynamic and only determined at runtime. The sample demoed during the webinar is a good example of this use case.
4) Speaking of, enough groundwork already! Show me some code. The webinar demoed a simple 'Top 10 open Opportunities' VF page with the Opportunities grouped by their respective Accounts and displayed in a tabbed format. Each tab on the page corresponds to an Account. Since the number of Accounts that the top 10 Opportunities could belong to is dynamic (could be a min. of 1 or a max. of 10), you can't create this page using static <apex:tabPanel> and <apex:tab> tags with 'rendered' attributes. Instead, you can use a Dynamic VF component and insert the appropriate number of tabs at runtime.
Here is the VF markup for the page.
And the corresponding Apex controller
Lets walk-through the code. The VF markup is super simple – which is after all one of the reasons for using Dynamic VF components. The entire Tab Panel section of the page is represented with a single <apex:dynamicComponent> tag whose 'componentValue' attribute is linked to the 'getTabbedView' controller method that returns the dynamic VF markup at runtime.
Lets now look at where the real action is – the 'getTabbedView' controller method. Every standard VF tag (except for certain tags that aren't currently supported in Pilot) now has an equivalent Apex class representation – Component.Apex.<Component Name>. So for example the <apex:dataTable> tag is represented by Component.Apex.DataTable, <apex:TabPanel> by Component.Apex.TabPanel and so on. Every attribute that exists on a standard Visualforce tag is available as a property in the corresponding Apex class (e.g. the 'title' attribute of the TabPanel component).
You generate dynamic VF markup in Apex by instantiating and manipulating these classes. Adding child nodes to a dynamic Visualforce component can be done via the 'childComponents' List property. That is exactly what the 'getTabbedView' controller method does (line 35) – generate a TabPanel component and its child Tab panels based on the runtime Opportunity data. You can also see how it's possible to insert HTML markup in a dynamic VF component by using Component.Apex.OutputText with the 'escape' attribute set to false. Finally, the 'getOppTotal' method (line 71) shows how you can use the 'expressions' property to set expressions, formulas and global variables (like '$User' etc.) in a dynamic VF component.
Sorry for the seemingly endless post and congratulations for making it this far! Remember to also check out the Summer' 11 home page for additional documentation and other resources for the upcoming release. Happy coding and as always, comments and questions are welcome.