Butterknife: It's not clear if ButterKnife.unbind is required for fragments

[lorenzos]

Documentation states:

Fragments have a different view lifecycle than activities. When binding a fragment in onCreateView, set the views to null in onDestroyView.

To me, it's not clear if this is strict requirement or not. I never implemented onDestroyView in my fragments, because the system is supposed to clear view references itself when fragment is destroyed in onDestroy. So:

1) Does documentation just suggest to do so, in order to force garbage collection of those views (a good practice for someone)?

2) Does ButterKnife require it because it handles views in such a way that there is a memory leak risk in fragments (eg. Fragment.setRetainInstance or similar)?

[egor-n]

There can be a case when fragment's view is destroyed, but the fragment instance is still present. For example, when fragment goes into the back stack - onDestroyView() is called, but onDestroy() is not.

[artem-zinnatullin]

"System" will not clear view references in onDestroy(), they're just regular references and they would be freed only if GC will collect them. So for example if you have long running async code with strong reference to the Fragment, GC won't collect bonded view objects until there won't be strong references to the Fragment and you'll have memory leak which would keep not only Fragment itself but also bounded Views.

Calling unbind() in onDestroyView() is not required, but recommended.

But you should also keep in mind that if you don't prevent async callbacks that work with bounded Views after onDestroyView() app could be crashed by NullPointerException because of nulled View references.

[lorenzos]

@artem-zinnatullin @egor-n Thanks for the clarifications.

@artem-zinnatullin About the async stuff, sure!, I always check views still exists in my callbacks.

[JakeWharton]

It is not required for ButterKnife. The code does not care whether or not you do this. As to fragments, I'm not sure if it's strictly required or not as I don't use them and never cared to look. The documentation certainly seems to indicate that it's something you should do.

[lorenzos]

@JakeWharton Thank you. I'll surely try ButterKnife in the next company's project! :hocho: