Hello Jean-Noel,
Am 28.04.2009 um 16:11 schrieb Jean-Noël Rivasseau:
Hi Martin and thanks for the answers, which result in more
questions :)
Hi,
I had a look at the data binding framework of Qooxdoo which looks
great and promising. I have a question though, it looks like there
is some support for pulling data out of a data source and then
binding it to a view widget via the Json store class, then the
controllers. But is the other direction possible, eg, detect a
change to the model which was bound to a widget, and automatically
make a server call back to the web server to update the data source
(probably a relational DB).
Sure that is possible. But we dont have a store ready for it yet.
You can see an example for writing data back from the model in the
gears demo in the demo browser. Specially for such a scenario, a
bubble event mechanism has been introduced to the generated models.
That way you dont have to listen to every single value in the model.
You can take a look at the API or the code to see how it works:
http://demo.qooxdoo.org/devel/apiviewer/#qx.data.marshal.MEventBubbling
I've looked at this and MEventBubbling seems the way to go. However
I am not quite sur how to use it. In the Gears demo you just create
a class from some result JSON data via the marshaller and add an
option so that the generated class automatically implements this
mechanism. How can I do this with one of my own class? I can add the
MEventBubbling mixin, but the API say:
If you want to use this in your own model classes, be sure that
every property will call the #_applyEventPropagation function on
every change.
How do I do this? Manually writing my own setter that will call this
function? Doesn't it defeat the purpose of having this mechanism? I
mean, if I have to write all my setters functions, I may as well
make them call the final method that will update the model back into
the server via a server call.
If you want to use the MEventBubbling mixin you have to call that
method on every change. The way i did it in the generated classes is
to use this method (__applyEventPropagation) as apply on every
property, which you can add easily with the apply key in the property
definition. If you already have an apply method, just call the method
in your apply and you should be fine. The advantage of using he
bubbling is that the events will bubble up the object hierarchy. Thats
an huge advantage to implementing the actual function code in the
objects.
Of course, such an automatic change may cause some problems, so it
should be configurable I guess (only update when the user presses a
specific button for instance). I guess I could also manually code
something up pretty quickly thanks to Qooxdoo events launched on the
model (writing code on _apply for instance), but I was wondering,
has anyone thought of this functionality? It would be nice if it
were implemented in a way which makes sense.
Sure we have thought of that. Its on our todo list to get something
in that direction out of the box.
Ok, I will wait until you are a bit more advanced on this then.
Second question, because of cross domain concerns, I am using the
script implementation when making server calls. Is this option
available when using the Json store? Eg, is it possible to use the
current Json store with a server call via a script transport
implementation.
It is possible but not right out of the box. Just take a look at the
twitter or flicker demo in the demobrowser. Each of them uses a
special store implementation and a other object for transport (both
use JSONP). I guess exactly the same way you could change the
transport layer.
Ok, haven't looked at that yet but I will soon.
Third question, the docs about using a delegate for data-binding
don't mention how to actually use the delegate with the
controller ?! Eg, once you wrote your delegate, how do you hook it
up in your controller?
The lists and tree controller support the delegation mechanism. Both
of them have a property called delegate where the created delegate
object should be set via setDelegate(...). Thats all. :)
Ha ok. I only looked at the simple Object controller and it did not
have that property, thus my confusion. So you cannot use a delegate
with the Object controller? Why? (I currently only use Object
controllers).
The delegate offers three methods to manipulate the creation of the
widgets of the controller and a fourth method for filtering the
content. The object controller does not create objekts like for
example the list controller creates listitems. Also the filtering
could be a problem on the object controller. I dont see how to filter
singe values. Therefore, the whole delegate would not offer additional
functionality to the object controller and has been due to that left
out.
Last question, I am interested in the hierarchy data binding ("A
more advanced feature of the single value binding is to bind a
hierarchy of properties to a target property.")
However, conceptually, with a complex model, there could be more
than one child for the parent object.
Eg, how would you adapt the current following code to a case where
a has a "b" node but also a "c" node with a different property?
Does not look possible currently...
var a = new Node("a"); // set the name to „a“
var b = new Node("a"); // set the name to „b“
a.setChild(b);
// bind the property to a labels content
a.bind("child.name", label, "content");
The binding always goes down from one property to another. If you
change something in the chain, the binding tries to get down the new
property chain. If thats not possible, the target property will be
reseted.
I did recently a presentation on the whole data binding layer.
Perhaps the slides could make the concept of the "deep binding"
better understandable. You can find the slides on my slideshare
account. http://www.slideshare.net/wittemann/data-binding-in-qooxdoo
For this I think you did not really understand my question. Let's
imagine that we have an object myZoo of the class Zoo. Zoo has two
properties lion, and elephant.
You are right, but now i get your question. ;)
How could I bind myZoo.lion.age to a GUI widget (like a slider), but
at the same time bind myZoo.elephant.age to another slider widget?
If I do myZoo.setChild(lion); then I guess it has no sense writing
myZoo.setChild(elephant) because I already declared a child - but
myZoo in effect has multiple children!
In the
myZoo.bind("child.age", slider, "value");
call, which child will be used?
Your example itself is some kind of misleading. If you have a myZoo
object which does have two properties (lion and elephant) you will
have to use this properties to set the objects. So myZoo.setChild
adresses a third property called child. If you want to set the lion
property, you have to use myZoo.setLion(lion) and the same for the
elephant: myZoo.setElephant(elephant).
That way, you have two properties set to two different objects. This
could be used in the binding as well:
myZoo.bind("lion.age", slider1, "value);
myZoo.bind("elephant.age", slider2, "value");
If you want to use only one property and swith the animals on runtime,
you can du that with the mentioned child property (or call is
something else, it doesn't matter).
myZoo.bind("child.age", slider, "value");
myZoo.setChild(lino); // lions age is bound to the slider
myZoo.setChild(elephant); // elephants age is bound to the slider
So it depends on what you want to achieve.
Regards,
Martin
Do you see what I mean?
Cheers
Jean-Noel
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