Implement lifecycle hooks for directive/component controllers (ng2-style)

[gkalpak]

I open this issue in order to track/discuss the implementation of lifecucle hooks to directive/component controllers.

Context

In our attempt to improve the upgrade path to Angular 2, it makes sense to allow developers structure their directive/component controllers is a way that is as easy as possible to migrate them to Angular 2 (ideally, there should be no modification of the controllers code necessary).
As part of this attempt, it will be useful to implement some of the lifecycle hooks available in Angular 2. (Obviously, it isn't necessary (or possible) to implement all of them, due to differences between ng1/ng2 internals.)

Lifecycle Hooks

• OnInit: Implemented in v1.5.0 as $onInit.
• OnDestroy: Useful (and probably straightforward to implement). Discussed in 1.5 Feature: Backport ngOnDestroy (as $onDestroy for example) exactly as ngOnInit ($onInit) #14020.
• DoCheck: Not applicable. Applicable. (See feat($compile): backport $doCheck #14656.)
• OnChanges: Not applicable. Applicable.
• AfterContentInit: Not sure how much more useful than AfterViewInit (in the context of ng1).
• AfterContentChecked: Not applicable.
• AfterViewInit: Useful. Discussed in FormController: attach to component controller? #13991.
• AfterViewChecked: Not applicable.
• PostLink: Angular 1 specific.

UPDATE:
Since we can't match the semantics of AfterView/ContentInit closely enough, we implemented a $postLink hook instead, which is close (but not the same) and fits ng1 semantics better.

[thorn0]

Why is OnChanges not applicable?

[gkalpak]

I'm not sure what I was thinking at the time. Maybe because it's tied to Inputs/Outputs and ng1 doesn't have the same semantics. It would probably be reasonably feasible to implement for '@' and '<' as inputs and '&' as outputs (with a small overhead), but with two-way binding it gets really muddy.

But I can definitely be convinced otherwise. One of the main purposes of opening the issue was to get the discussion going.

[thorn0]

I'm not sure if OnChanges works with outputs at all. Even though the docs state otherwise:

ngOnChanges - called when an input or output binding value changes