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There are many questions here dealing with This class should be static or leaks might occur in java android.

This Handler class should be static or leaks might occur: IncomingHandler

This Handler class should be static or leaks might occur:AsyncQueryHandler

This AsyncTask class should be static or leaks might occur (anonymous android.os.AsyncTask)

The warning is due to the fact that inner class holds an implicit reference to the outer class, and hence preventing the outer class from GC'd. The solution lies in the warning itself that the class should be declared static.

However, the solution is java specific. Given that kotlin has no static modifier, the closest thing is companion object and companion object does hold reference to it's "outer class".

Below are my [failed] attempts with remarks

class MyActivity : AppCompatActivity(), MyListener {

    companion object {
        class Attempt3Task(val callback: MyListener) : AsyncTask<Unit, Unit, Unit>() {
            override fun doInBackground(vararg params: Unit?) {
                TODO("")
            }

            override fun onPostExecute(result: Unit?) {
                callback.updateUi()
            }
        }
    }

    inner class Attempt2Task : AsyncTask<Unit, Unit, Unit> () {
        override fun doInBackground(vararg params: Unit?) {
            TODO("
        }
    }

    // Gives warning "This AsyncTask class should be static or leaks might occur"
    val attempt_1 = object: AsyncTask<Unit, Unit, Unit>() {
        override fun doInBackground(vararg params: Unit?) {
            TODO("")
        }
    }

    // Does not give warning but, as far as I can tell, is conceptually same as attempt_1
    val attempt_2 = Attempt2Task()

   // Does not give warning but companion object does have reference to the activity, no?
    val attempt_3 = Attempt3Task(this)

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
    }
}

Are the assertion about attempt2 and attempt3 correct that even without the linter warning, the code is still leaking?

What options do we have to avoid the leaking? Should I resolve to plain old top-level class MyTask : AsyncTask<Unit, Unit, Unit> () with a member of WeakReference to callback?

user2829759
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  • I'd like to say `AsyncTask` should be as local as possible. so all the code above are wrong usage. which means dispose/release it immediately after used. – holi-java Jun 27 '17 at 07:30
  • Nested classes in Kotlin are equivalent to `static class` in Java by default - did you try dropping the `inner` keyword of `Attempt2Task`? See https://kotlinlang.org/docs/reference/nested-classes.html – JK Ly Jun 27 '17 at 07:30
  • @JK Thanks for pointing out! I have read the `inner classes` section multiple times without realising it is implied that nested classes has no access to member of outer class! – user2829759 Jun 27 '17 at 07:43
  • `Attempt3Task(this)` has a reference to the activity as well. You're only providing it explicitly as the callback. – tynn Jun 27 '17 at 09:27
  • I'd like to advice you to declare your `AsyncTask` in java file as static class and then use it from kotlin. – A. Shevchuk Jun 27 '17 at 10:14
  • and another option: have you tried to make nested `AsyncTask` `internal` visibility? Seems like it won't have a reference to root class – A. Shevchuk Jun 27 '17 at 10:26
  • The `inner` portion seems to be the issue here. Having it as just a nested `class` should be fine, as with putting it in another file. Likewise, have you looked into other solutions? Kotlin has an experimental [coroutines](https://kotlinlang.org/docs/reference/coroutines.html) function set as well as [anko](https://github.com/Kotlin/anko) which may help you deal with async tasks with ease. – Allan W Jul 01 '17 at 20:49
  • You should try this answer: https://stackoverflow.com/questions/44309241/warning-this-asynctask-class-should-be-static-or-leaks-might-occur – Aashish Kumar May 25 '19 at 08:54

1 Answers1

1

Why don't you have the AsyncTask class declaration outside of the activity class?

In Kotlin that could be in the same file as the activity but just above/below the Activity class.

That way there is no issue about a hidden reference.

Also make sure to just keep a WeakReference to the listener inside your AsyncTask.

That said, according to me, AsyncTask belongs to the past, and you should now be using some more modern alternatives such as RxJava, co-routines, Loaders, etc.

Vincent Mimoun-Prat
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