You have the right idea; to encapsulate the dataProvider, validation and change
event handler. But, instead of putting them inside the control, wrap all of
that into a common facilities model, that gets used anywhere it's needed in the
application. I stopped using Cairngorm a long time ago, but hopefully the
newest version supports dependency injection; so you can just inject a
reference to the facilities model where needed, and hook it up to the combo
box. That would be best practice. But, at the end of the day, the goal is to
make it work, so...
-TH
--- In flexcoders@yahoogroups.com, "hanzo55" <shawn.a.holmes@...> wrote:
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> I very much appreciate the help! Any chance I can take to improve the design
> would be greatly beneficial, from a maintenance standpoint.
>
> My feeling originally was if I have two comboboxes that are in entirely
> different parts of the app, but that will always be populated by the same
> data provider, always have the same validation and always utilize the same
> change function (while being different from other comboboxes in the site), it
> made sense to encapsulate the dataprovider/validation/change events into the
> box itself so it could be added to a view without having to specify all of
> the various attributes a combobox needs--since they are not changing.
>
> Initially, it seemed a bit pointless to write:
>
> <components:FacilityComboBox dataProvider="{model.facilities}" />
>
> everywhere I implemented the Facility ComboBox since everywhere the Facility
> ComboBox is implemented...the dataProvider is *going* to be model.facilities
> and will never change.
>
> If you think that there is a good example somewhere that demonstrates a
> better design for this type of class hierachy, please point me to it and I'll
> have a look. As the subject states, I'm very much looking for the best
> practice here.
>
> --- In flexcoders@yahoogroups.com, "turbo_vb" <TimHoff@> wrote:
> >
> > Validation can be abstracted just like dataProviders. For a combo box, you
> > only need to validate the selectedItem; from the view, presentation model,
> > or a common utility class. Most other stuff happens in itemRenderers; that
> > have a little more freedom. It may be that you're locked into a structure
> > that was handed to you, but hardcoding a reference to a singleton model,
> > from which you set the data provider of a combo box from within the combo
> > box, breaks the rules. If you're having problems with binding the
> > dataProvider to the model's property, the binding problem is probably
> > upstream from the combo box. Good luck Shawn, just trying to help.
> >
> > -TH
> >
> > --- In flexcoders@yahoogroups.com, "hanzo55" <shawn.a.holmes@> wrote:
> > >
> > >
> > >
> > > There's more to the story in regards to the class design than what's
> > > provided here; The subclass is actually part of a larger set of classes
> > > that share common functionality in terms of their validation and change
> > > events based on the data-providers for a global app.
> > >
> > > That common functionality is centralized in their parent class. The
> > > dataProvider assignment in the constructor is tying those specific
> > > ComboBox subclasses to a family of service providers that produce an
> > > expected set of columns. Since those ComboBoxes, with their very specific
> > > validation and change routines (which are common to each other), apply
> > > very tightly to those service providers and no others, it made sense to
> > > subclass them and encapsulate dataProvider assignment, so those
> > > ComboBoxes could be used in any views that apply to that family of
> > > services.
> > >
> > > ...if that makes sense.
> > >
> > > --- In flexcoders@yahoogroups.com, "turbo_vb" <TimHoff@> wrote:
> > > >
> > > > Can't see any good reason to subclass a control in order to hardcode
> > > > the dataProvider. The idea is to keep the components loosely coupled.
> > > > Are you having a problem with dataProvider="{model.facilities}"?
> > > >
> > > > -TH
> > > >
> > > > --- In flexcoders@yahoogroups.com, Alex Harui <aharui@> wrote:
> > > > >
> > > > > Binding a visual component to a singleton limits its reuse. So there
> > > > > may not really a best practice. The minimum code way is probably to
> > > > > assign the dataProvider in commitProperties instead of the
> > > > > constructor. The model.facilities might have its final assignment by
> > > > > then.
> > > > >
> > > > >
> > > > > On 8/25/11 9:41 AM, "hanzo55" <shawn.a.holmes@> wrote:
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > I am working with a project already in place. It uses Cairngorm and
> > > > > is built on Flex 3.0.2.2113
> > > > >
> > > > > A standard ComboBox is implemented in one of the views like so:
> > > > >
> > > > > <mx:ComboBox dataProvider="{model.facilities}" id="Facility">
> > > > >
> > > > > "model" is a bindable singleton, and one of its properties,
> > > > > "facilities" is a public ArrayCollection. On initialization, a
> > > > > function runs in the singleton to populate facilities; it does this
> > > > > by pointing model.facilities to another ArrayCollection that has been
> > > > > previously populated, such as:
> > > > >
> > > > > model.facilities = model.assigned_facilities;
> > > > >
> > > > > This works without issue; when the application starts, the ComboBox
> > > > > is properly populated with the values pointed to by model.facilities.
> > > > >
> > > > > I have decided! to come in and build a subclass of ComboBox in
> > > > > ActionScript, and rather than pass the dataProvider in, I want to
> > > > > include the singleton within the ActionScript, and simply do the same
> > > > > assignment in the constructor. The resulting MXML would look like
> > > > > this:
> > > > >
> > > > > <components:FacilityComboBox id="Facility" />
> > > > >
> > > > > and the constructor would look like this:
> > > > >
> > > > > public function FacilityComboBox()
> > > > > {
> > > > > super();
> > > > > ! BindingUtils.bindProperty(this, "dataProvider", model,
> > > > > "facilities");
> > > > > }
> > > > >
> > > > > My question is: Is this the best practice when subclassing a
> > > > > UIComponent and wanting to handle the dataProvider assignment
> > > > > internally? The reason I ask is, I had originally built the
> > > > > constructor like this:
> > > > >
> > > > > public function FacilityComboBox()
> > > > > {
> > > > > super();
> > > > > thi! s.dataProperty = model.facilities;
> > > > > }
> > > > >
> > > > > which worked for other subclassed ComboBoxes where the dataProvider
> > > > > *did not change after initialization*. However, because of how
> > > > > model.facilities is assigned (to an existing ArrayCollection), no
> > > > > change was ever detected, and upon launch the application, the
> > > > > ComboBox sat dormant and never received any values to populate.
> > > > > Changing to the BindingUtils method solved this problem, but I now
> > > > > fear I'm missing a much broader concept about dataProvider assignment
> > > > > in pure ActionScript classes. Is my BindingUtils methodology the one
> > > > > to go with? Or should I be considering something drastically
> > > > > different?
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > --
> > > > > Alex Harui
> > > > > Flex SDK Team
> > > > > Adobe System, Inc.
> > > > > http://blogs.adobe.com/aharui
> > > > >
> > > >
> > >
> >
>
