Notify of _subController property change

[bcardarella]

When ArrayControllers instantiate an itemController and insert into the
_subControllers array the member it replaces is undefined. This fix
will push a notification for property change when the actual
itemController replaces the undefined item.

[bcardarella]

I was not sure how best to test this one out, open to suggestions so a regression test is in there.

[wycats]

In general, we don't notify _ properties. Could you explain the use-case a bit more?

[bcardarella]

ember-validations is being rewritten to observe isValid flag on all children. The && of all isValid flags in the validator graph for an object will be the value of the object's isValid. Validation rules can be defined in the models themselves but I am recommending that the rules be defined in the controller. For this issue if the validations are set in the itemControllers then when those itemControllers instantiate the parent controller is not being notified of that and the validation graph is reporting false values as the observer for those items is firing when the undefined is inserted in the subController array.

[bcardarella]

@wycats the other option is to add the instance of the itemController directly to _subControllers instead of the undefined placeholder.

[wagenet]

@wycats, thoughts?

[wagenet]

@wycats ping

[bcardarella]

Bueller?

[hjdivad]

@bcardarella do you happen to have a jsbin that illustrates this problem?

[bcardarella]

Here are the tests and workaround I did for ember-validations: DavyJonesLocker/ember-validations@00a775e

[hjdivad]

see DavyJonesLocker/ember-validations#102.

I believe the tl;dr for ember here is that users should, whenever possible, ignore the implementation detail that an array controller happens to be presenting items behind item controllers, and instead treat the array controller as any other kind of array for the purposes of observers, CPs &c.

So if, for example, one wants to observe changes to arrays, add observers to the [] property.

[bcardarella]

Closing. @hjdivad your suggestion is better, thanks!