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
> >
>
