Docs for NgAttachAware and NgDetachAware not useful

[yjbanov]

The docs for NgAttachAware and NgDetachAware are too fuzzy to be useful. It makes it hard to rely on any sequence of events.

NgAttachAware

/**
 * Implementing directives or components [attach] method will be called when
 * the next scope digest occurs after component instantiation. It is guaranteed
 * that when [attach] is invoked, that all attribute mappings have already
 * been processed.
 */

Issues:

• In Dart, instance methods can only be called after instantiation, so this part is not useful, unless you are referring to some other definition of "instantiation". I think you are trying to say "the first scope digest".
• In "when the next scope digest occurs" the "when" doesn't actually tell me if it will happens immediately before, immediately after or at a certain point in the middle of the scope digest.
• "all attribute mappings" seems to mean ones declared by the implementing component via @NgComponent or annotations, such as @NgTwoWay. However, I'm also observing that Angular calls the getters on my component that are bound in the template of this same component, before calling attach. Could this be a bug?

NgDetachAware

/**
 * Implementing directives or components [detach] method will be called when
 * the associated scope is destroyed.
 */

Issues:

• Same problem with the word "when" as the one in @NgAttachAware.

[pavelgj]

I'm also observing that Angular calls the getters on my component that are bound in the template of this same component, before calling attach.

This is actually a side-effect of the new change detection, and so far it's not clear if there's a way around it. The change detection was designed to work with other change detection systems like Object.observe or package:observe, which are not aware of angular directive/component lifecycle. Maybe this deserves a separate issue -- it's not really related to NgAttachAware/NgDetachAware.

[yjbanov]

I agree that investigating whether "getters called prior to attach" is a feature or a bug might warrant a separate issue. However, it is still related to NgAttachAware and NgDetachAware, as these are life-cycle callbacks, and app developers need to know when their getters are called w.r.t. the component's life-cycle.

I've been treating the attach() method as something that separates the "setup phase" from "render phase". In the "setup phase" my component is instantiated, injected, attributes are bound (i.e. my setters are called). Only after this phase do I have the state from which to prepare the component for rendering of the template. If the rendering starts before then, my component is not ready and Angular may get errors or corrupted data if it calls my getters. A common workaround is to add checks and guards in the code, but it pollutes the code.

I think the documentation should be crystal clear about the meanings of "attach" and "detach". This way I will know when Angular will call into which code of my component and I can make sure the component is ready.