Recursively extending child in selectable list for nested lists

[gobadiah]

I'm using the selectable enhancer on a nested list, but for now only top ListItem can be selected.

With this pull request, we recursively modify children and their nestedItems props to make every ListItem selectable.

This is my first pull request so I may be doing this wrong, any advise would be gladly taken.

Thanks !

[oliviertassinari]

@gobadiah Looks good to me. Could you fix the travis task?
@frankf-cgn Could you review this too?

[gobadiah]

Yep, done.

[oliviertassinari]

If we can, could you move this method outside the render method?
That's going to be better for perf. We don't want this to be allocated at each rendering.

[oliviertassinari]

@gobadiah Looks good now. I could merge it as it is 👍.
However, if you want this to be less likely to break in the future, I would recommend you to update the SelectableContacts example with this feature (that's not as good as a test, but still).
It would help to keep track of this.
And to be perfect, you can squash down the commit to keep a clean history.

[gobadiah]

@oliviertassinari I've updated the example SelectableContacts. Just a remark:
If you select a nestedItem, and then "toggle" its parent, the nestedItem is still selected but no longer visible.
It seems to me this shouldn't be the normal behaviour, so maybe when that happens we should call requestChange props with null for example, or notify the user in some way.
In my case, the selectedItem plays an important role, so I have to watch toggle event, and search the tree to see if the selectedItem is now hidden, it must be easier to do this in the library.

[frankf-cgn]

@oliviertassinari @gobadiah So far looks good to me, too. But before merging, we should solve the toggle-issue mentioned by @gobadiah.
I have no immediate idea for a smart solution at the moment. (Re-)Setting the selectedItem because of the parent-toggle does not seem right to me. My first though on it is that it might be better to mark the parent somehow, indicating that tehre are hidden selected items. @gobadiah: What do you think? Is marking the toggleable parent an option?
If it helps, I could investigate on this on wednesday.

[gobadiah]

@frankf-cgn Tagging the parent listitem seems a viable option, though I have no idea how to do this "visually". I still think a user should be able to know when that happens, so he can respond according to his use case, by doing nothing, or maybe deselecting, or whatever.

[oliviertassinari]

If you select a nestedItem, and then "toggle" its parent, the nestedItem is still selected but no longer visible.

I think that there are valid use cases for this.

(Re-)Setting the selectedItem because of the parent-toggle does not seem right to me.

I agree, for instance, have a look at the List menu on the left panel of https://material.angularjs.org/latest/.

But before merging, we should solve the toggle-issue mentioned by @gobadiah.

Well, I think that this PR is already valuable and that we are talking about a missing feature,
not about a wrong implemented feature. I'm gonna merge.

@gobadiah Thank!