Previously, I have written about Grid’s new WebService running mode, which allows Grid to communicate with an ASP.NET AJAX web service directly from the client, and do all its data loading through it, including paging, sorting, filtering, etc. This powerful functionality is also available on ComponentArt navigation controls: TreeView, Menu, NavBar, TabStrip and ToolBar. All of these have the ability to load their data from an ASP.NET AJAX web service. TreeView, furthermore, has the ability to load data for each node on demand. Since this functionality is a superset of the simple ability to fetch all the data at once, I’ll outline the more complex case here.

- On the server, we use the WebService and WebServiceMethod properties to set the name of the registered web service to use, as well as the name of the method to invoke to retrieve node data.

- The service WebMethod refered to by the control’s WebServiceMethod property should be implemented with the following signature:

public TreeViewWebServiceResponse MethodName(TreeViewWebServiceRequest request)

The above example is for TreeView – for other controls, the appropriate types should be used, eg. TabStripWebServiceResponse and TabStripWebServiceRequest for TabStrip.

- The method’s return value (a *WebServiceResponse) should contain the nodes to be sent to the control.

At this point, the work of defining a web service data source for a navigation control is complete. With the above setup, the control will fetch its data from the specified web service by invoking the specified method.

With TreeView, we often wish to configure data loading using an on-demand mechanism. This means that a node’s children are loaded only when that node is expanded and no sooner. To achieve this, we only need one additional step:

- Instead of populating a TreeViewNode with its child nodes, set its UseWebService property to true to specify that the web service should be used to fetch its child nodes. When this is done, the same WebServiceMethod will be invoked as for the root nodes, but the TreeViewWebServiceRequest’s Node property will be set to the TreeViewNode which needs to be populated.

That’s all there is to it.

Note: All the navigation controls also have a WebServiceCustomParameter which can be set on the server or the client, and which is sent back as part of every *WebServiceRequest. This should allow for custom context-dependant data loading.

For a simple demo of this functionality, check out the Web Service Creation sample on our site. For a look at web service-driven TreeView load-on-demand, take a look at this TreeView sample. A useful real-world application using TreeView and Grid, build entirely on web services, can be seen in the Full Web Service Application sample.