The PagingMethod property enables you to specify how paging requests are handled. The default setting is PostBack, which posts each page request back to the server. You can change the setting on the Web Generation page in the Properties view with the Format to Configure set to HTML/XHTML.
CallBack paging uses a script callback feature to provide page navigation without posting the whole page back to the server. The XML data for the next requested page is downloaded as an XML string returned to the callback. A JavaScript function on the client collects the data and invokes the client-side XSLT processor to transform the data using the XSLT stylesheet that was downloaded and cached on the first request. The next page of data is displayed on demand. If you set the PagingMethod property to CallBack, you do not need to write server-side code and client-side JavaScript to take advantage of the script callback feature.
For the XML rendering format, the design of the Callback! option requires that a reusable XSLT stylesheet be generated so that the browser can cache it. The benefit from this requirement is that only the XML data for the next requested page need be returned by the callback. This XML data is always trivial in size (about a 1 to 20 ratio), resulting in significant bandwidth savings. This is unlike other implementations, where the entire presentation is always regenerated and downloaded again from every callback.The generated XSLT stylesheet is not reusable, and therefore cannot be cached by the browser, if the DataWindow layout is inconsistent page-to-page, or it does not contain a complete first page of data. In these scenarios, the Callback! option defers to PostBack! until a stylesheet can be generated that is reusable, and can therefore be cached in the browser.
When the PagingMethod property is set to XMLClientSide, the page takes slightly longer to load on the first request because all the data in the result set is pulled down to the client, but subsequent paging requests take place entirely on the client. InsertRow, AppendRow, and DeleteRow actions take place on the client with no postback or callback to the server. However, any computed fields in the DataWindow that rely on the RowCount method are not reevaluated until the user performs an action such as an Update or Retrieve that forces a postback to the server.
Client-side paging is available only for the XML rendering format and in button actions and client JavaScript paging functions of the Web DataWindow client control.
