On Wed, 30 May 2007 12:58:48 +0300, kgi wrote:

On Wednesday 30 May 2007 02:25:23 Jean-Paul Calderone wrote:

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On Wed, 30 May 2007 01:44:07 +0300, kgi wrote:

Hi Jean-Paul; thanks yet again for chiming in with a timely response.

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This is like trying to call an unbound method in Python. What you really want to be doing is calling chain on an /instance/ of XCall.B, not on the class object itself.

I see what you mean. I *thought* I was just mimicking the approach used in lots of the Nevow code itself, but now I see The Error Of My Ways. Just to make sure that my insight is not bogus, can you comment on the "truthiness" of the following statements:

Sure.

1. When a LiveElement is rendered, it is assigned an Athena Id (probably server-side) and something in the Nevow runtime creates a class *instance*, identifiable and accessible from the server through the magic of the Athena Id. In other words, there is rarely (never?) direct instantiation in JS code of objects ("var f = new Foo()") when the classes are Athena subclasses.

Yep. To be specific, "Nevow.Athena.Widget subclasses", though I don't think there are any other interested classes in the Nevow.Athena namespace. ;)

2. If I instantiated N LiveElements of the same class, all N would be individually accessible from the server just by calling object.callRemote().

Right. Each server-side LiveElement instance is tangled up with its corresponding client-side Nevow.Athena.Widget (subclass) instance, and vice versa.

3. However, whereas server->client calls have implicit access to the Athena Id, so the callRemote() can be routed accordingly to the right instance, client-side Javascript doesn't have this.

Roughly correct, but see below.

I think I was confused by the fact that up until now I've only been having one LiveElement instance of each type on a page, so I never had to think about object disambiguation.

If this is the case, then I need a way of informing *client* side objects how to find each other. In other words, I need to embed the callee javascript object's Athena Id into the caller, either at creation time, or later. Is this a "done thing"?

(Either that, or I go via the server)

Widgets on the client have a hierarchical relationship with each other which reflects the hierarchical relationship of their corresponding server-side LiveElement progenitors. That is, if LiveElement B has setFragmentParent called on it with LiveElement A as an argument, then Widget B will have a widgetParent property which refers to Widget A; similarly, Widget A's childWidgets array property will include widget B. These relationships can be used to pass messages between widgets in the browser without involving the server.

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Also, I'd recommend not clobbering XCall.A and XCall.B with your class objects, since those are set up to be module objects because they each have a corresponding .js file. Athena's module system tries to mimick many aspects of Python's - in this case, XCall corresponds to a package, XCall.A and XCall.B are modules in that package, and you want to be defining things like XCall.A.Foo and XCall.B.Bar as attributes of those modules.

Ah, I see. You mean that the very existence of the files XCall/A.js sets up the (empty?) XCall.A namespace, and within XCall.A.js I define classes like:

XCall.A.Foo = Nevow.Athena.Widget.subclass ( 'XCall.A.Foo' );

Yep.

Thanks again for your help, Jean-Paul, I know how busy you guys are. I'm sorry if it takes two or three attempts to get my head round some of the muddier aspects of how it all fits together - it's all pretty new and unfamiliar.

No problem. :) Hope this helps, Jean-Paul

On Wed, 30 May 2007 17:53:11 +0300, kgi wrote:

On Wednesday 30 May 2007 15:15:56 Jean-Paul Calderone wrote:

Hi Jean-Paul; thanks for your email - very helpful.

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Widgets on the client have a hierarchical relationship with each other which reflects the hierarchical relationship of their corresponding server-side LiveElement progenitors. That is, if LiveElement B has setFragmentParent called on it with LiveElement A as an argument, then Widget B will have a widgetParent property which refers to Widget A; similarly, Widget A's childWidgets array property will include widget B. These relationships can be used to pass messages between widgets in the browser without involving the server.

Yep, I see the attributes for traversing along the hierarchy. Unless I've misunderstood, in order for a widget's Javascript to be able to call another widget's Javascript, it has to do something like:

self.widgetParent.widgetParent.widgetParent ... childWidgets[0].childWidgets[1].doStuff()

This feels somewhat wrong, partly because of fragility: if I move the location of a widget in the hierarchy, its Javascript code will need updating.

Yep. One solution to this is to do something like: self.widgetParent.doStuffToSpecificThing() Supplying an implementation of doStuffToSpecific for whatever the widget's parent happens to be which knows about its position in the overall page layout. This keeps the inter-widget dependency limited to a single step.

Is there a way of accessing another widget in the page directly by name? An example might be a panel where I want any widget to be able to append status messages.

I would imagine this might entail assigning a user-controlled widget id to the top-level DOM node of a LiveElement (as opposed to *subnodes* of the widget, in which ids are rewritten for use by nodeById(), and which need the athena id to access).

I suppose the stan would look like this (this doesn't work, because the id gets clobbered by the autogenerated id):

T.div ( _id = 'my-unique-id', render = T.directive ( "mywidget" ) ), T.div ( _id = 'another-unique-id', render = T.directive ( "mywidget" ) )

Then in JS code of another widget:

w = self.getAthenaWidgetByName ( 'my-unique-id' ); w.doStuff()

Obviously, the LiveElement nodes are already all assigned a unique id, it's just that it's done automatically and there's no obvious way of getting at them ahead-of-time.

I guess I could always cheat and wrap all LiveElements inside named divs and do document.getElementById(), but that feels silly, given that the divs are already named.

There are plenty of methods in Nevow/nevow/js/Nevow/Athena/__init__.js for getting hold of things but they all seem to need either the *numeric* athena id (fromAthenaID, callByAthenaID) or a reference to a node (athenaIDFromNode, athenaClassFromNode).

Something about this approach rubs me the wrong way. Identifiers which are required to be globally unique sends one down the path of being limited to only supporting certain page configurations. Maybe if there were some well defined algorithm for choosing the "nearest" widget with a given identifier, something could be worked out. I'm not too sure about this either, though. You can already do something like this, though, if the class name is a sufficient identifier for the widget you want (find the node with the right value for athena:class, then find the widget associated with the node). I tend to discourage this approach in favor of the one I gave at the top of the message, though. Jean-Paul

Pardon me for jumping in here, but I think you're making this too hard. On Wed, 30 May 2007 09:53:11 -0500, kgi wrote:

Yep, I see the attributes for traversing along the hierarchy. Unless I've misunderstood, in order for a widget's Javascript to be able to call another widget's Javascript, it has to do something like:

self.widgetParent.widgetParent.widgetParent ... childWidgets[0].childWidgets[1].doStuff()

You can certainly do that, but there are plenty of other means of accomplishing this aim. For example, a widget has __init__() and nodeInserted() methods that you can override. If you want your widget instances accessible by some name known to you, then just do: self.widgetParent.someNameILikeToUseForThisParticularWidget = self; Better still, use a client-side event dispatching mechanism, and just let interested widget subscribe to a given "channel": MyDispatcher = { _subscribers: [], publish: function(channel, message){ ... }, subscribe: function(channel){ } ... }; Hopefully, this gives you some easier options to consider. -- L. Daniel Burr ldanielburr@mac.com