One method of implementing AJAX is to re-render the page and only send
pieces down to the browser. This is the way AjaxAnywhere works.
However, it is not easy to get this to work in MyFaces with HTML
forms. The issue:
AJAX needs a way to identify HTML to replace on AJAX response. This is
usually done via id:
"document.getElementById('idFromAjaxResponse').innerHtml =
reponseData".
However, there is no containing HTML element for the "special" form
elements. These "special" elements include:
1) input type="hidden" elements that are rendered for parameters,
client-side state, etc.
2) script tag that contains the clear_[formid]() JavaScript function
that uses the above hidden input elements
In 1.1.1, these were placed at the top and bottom of the form. In
1.1.2/3 they are put only at the bottom, but in neither is the
capability that I would like.
Workaround I used: Extended the HtmlFormRenderer and buffered the
output of the endcodeEnd and encodeBegin. Then I loop through the
buffer and strip out all hidden input elements and JavaScript tags. I
then add the stripped portion into a new SPAN element that is
formatted for AjaxAnywhere to work.
How this could have been much easier:
Add 4 new methods to HtmlFormRendererBase:
public void beforeFormElementsStart(FacesContext facesContext,
UIComponent component)
throws IOException {}
public void afterFormElementsStart(FacesContext facesContext,
UIComponent component)
throws IOException {}
public void beforeFormElementsEnd(FacesContext facesContext,
UIComponent component)
throws IOException {}
public void afterFormElementsEnd(FacesContext facesContext,
UIComponent component)
throws IOException {}
These methods would the be called:
encodeBegin(...) {
...render the start tag...
call before form elements start
...render and elements into the form
call after form elements end
...
encodeEnd(...) {
call before form elements end
... render state, javascript etc. ...
call after form elements end
... render the form end tag ...
Then, with projects like AjaxAnywhere, users can extend
HtmlFormRenderer and implement these methods. In these methods, we can
write tags to contain this data that can be used in the AJAX code to
update on every request.
This would be a very simple change, would incur almost no overhead and
give complete flexibility that would be needed to AJAX authors to have
control over the special form behavior of JSF.
I wouldn't care about the method names, in fact there could be one
method with an enum argument that specifies before/after information.
What do you think? If it sounds good, could this be added to current
before the next release? Since it would be just empty methods, it
would not de-stabilize the current code.
Thanks,
Andrew
