Caution with lateinit and Android

Android
1

lateinit vars seem to suggest itself for certain things when programming for Android, like:

  • fields for views that are available after they have been inflated in onViewCreated
  • fields for non-optional arguments that have been passed to the fragment in onCreate

I did it this way but now came across a race condition where a parent fragment would try to query a lateinit field of a child fragment (via childFragmentManager.findFragmentByTag(...)?.thatOneLateinitFieldThatIsInitializedInOnCreate and failed because the lateinit field was not initialized yet.

So apparently, a parent fragment can find a child fragment before onCreate on the child fragment has been called. This design makes it problematic to use any lateinit var for the above mentioned use cases.

2

Kotlin Is not Java, there is very little reason to keep using reassignable variables. Use lazy delegation and vals.

Have a look at this project for examples. The module ‘app’ is what you are looking for.

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3

I suppose you mean

private val foo: String by lazy { requireArguments().getString(ARG_FOO)!! }

Right, so lateinit can be avoided in this case. Though, this has the downside that it does not fail fast when a required argument is not passed (or something wrong is passed).

4

Well, the error you are trying to fix is not language related but resides in the logic of your application.
If the arguments are the ones needed to launch a fragment, use the Android navigator; if for an activity, check out how I statically parametrized the activity launch in the app I linked you.

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