[cells-devel] another redundant update

[Ken Tilton]

Andy Chambers wrote:
> Hi,
> 
> This was mentioned a while ago and is causing a problem now.  When an
> ajax request comes in, one of the things that gets updated is the
> input value.  For example...
> 
> old: <input name="term" value=""/>
> 
> ...user types in "progv" and hits TAB
> 
> new: <input name="term" value="progv"/>
> 
> We want the model on the server to update itself to reflect this
> change but we don't need to send it down to the browser because the
> browser already knows.  The problem this is causing (and this is
> something we'll need to take a mental note of for the future) is that
> the event binding for the input element is lost when that element is
> replaced.  That means any actions after the first don't trigger an
> ajax request.
> 
> We could rebind the event on the new element but I think its better
> not to send it in the first place.
> 
> I think this would apply to all UI elements so if that's the case, the
> solution is probably to filter updates containing these elements the
> same way that ascendant and redundant nodes get filtered in the code
> below.
> 
> 				  (let ((updt (loop for (h . xh) in (updates self)
> 						 unless (loop for (h2 . nil) in (updates self)
> 							   thereis (unless (eq h h2)
> 								     (when (fm-ascendant-p h2 h)
> 								       (trc nil "suppressing redundant" h :seeing-ascendant h2 (id h2))
> 								       t)))
> 						 collect xh)))
> 
> I've pushed a new version out to the repo but haven't dealt with this
> problem yet.

Lessee. The update happens in the observer on the xhtml slot, which is 
passed the clos instance for the node along with the old and new values, 
inter alia.

(defobserver xhtml ((self html))
   (when new-value
     (trc nil "new xhtml for" self)
     (assert (u^ web-app))
     (push (cons self (format nil "$(\"#~a\").html(\"~a\")" (^id)
                      (js-escape new-value)))
       (updates (u^ web-app)))))

I suggest you have an option or options on the clos node that controls 
whether the update gets sent:

(mk-input (:name "s" :id "s"
            :-type "text"
            :send :once ;; default t (other constraints possible,
                        ;; including a closure over other variables
                        ;; that returns t to send, nil not
            :any-more-info 'needed-t-control
            :value (c? (term (u^ web-apropos)))))

And then:

(defobserver xhtml ((self html))
   (when (and new-value (do-send self new-value old-vale))
     (trc nil "new xhtml for" self)
     (assert (u^ web-app))
     (push (cons self (format nil "$(\"#~a\").html(\"~a\")" (^id)
                      (js-escape new-value)))
       (updates (u^ web-app)))))

And:

(defmethod do-send (self new-value old-value)
    (bwhen (s (send self))
      (case s
        ((t) t) ; parens needed, long story
        (:once (not old-value))
        (otherwise ; better be a function :)
           (funcall s self new-value old-value)))))

Note I made it a method so one could just do:

(defmethod ((self input) new old)
    (not old))

That might be too extreme -- perhaps we /do/ sometimes need to get an 
input field out there again, perhaps with a different binding, or even 
to do symbol-completion (weird in apropos, but just as an example) -- 
but the flexibility might help someday. Maybe start with a defun and see 
if a GF is ever needed.

> 
> Another thing you might notice if you look at commented out code in
> the example is that the radio button at the bottom seems a bit
> verbose.  Radiobuttons could probably do with a layer on top providing
> a nicer way of creating them.  At the moment, user code has to create
> labels, manage the checked/unchecked status, and the value for each
> input.  It should provide something like celtk's mk-radio

I'll look at this next.

kt