A common scenario that our users encounter with the Grid is the need to populate it with different data depending on client-side context – for instance, a dropdown option or a TreeView selection. Very often, this situation is solved by to setting Grid to Server or Client running mode and wrapping it in a CallBack control, and then using the CallBack to send custom parameters back to the server and to refresh the Grid.
This has worked well for many, but is not without its limitations, mostly having to do with CallBack’s inability to maintain state across callbacks. It also seems somehow wrong and wasteful to approach things this way and completely ignore Grid’s own ability to issue callbacks, and maintain its own state.
To remedy this slightly awkward situation, we’ve introduced and small (but hopefully important) new feature to Grid as part of Web.UI 2007.2 SP1: the CallbackParameter property. This property can be set on the server or the client, and is sent back with every callback issued by the Grid. A Grid in CallBack running mode exposes this value on the server in time for every server-side event, and the value will mirror that on the client. So, where before we may have done something like this:
CallBack1.callback(‘mailbox’);
we would now do away with the CallBack control altogether, and do this instead:
Grid1.set_callbackParameter(‘mailbox’);
Grid1.callback();
Conditional logic on the server can then do the right thing based on the value of Grid1.CallbackParameter. To further facilitate this parameter-based loading, we’ve added two more server-side Grid events: BeforeCallback and AfterCallback. These are raised before and after (respectively) all the other events raised during a Grid callback request.
Hope you find this useful! Let us know what you think.
Note: This feature is available as of Grid 2007.2 SP1, available Dec 17. 2007.