Hi how can I access a generic type T for a class ``` abstract class TestCase lt T Activity gt val classz = javaClass genericSuperclass as ParameterizedType getActualTypeArguments 0 as Class lt T gt Rule JvmField val rule = IntentsTestRule classz false false ``` This seems to work to `open FooTestCase TestCase lt ActivityA gt ` but not to `BarTestCase FooTestCase`

Because the superclass of `BarTestCase` is `FooTestCase` which is not parameterized

Hi how can I access a generic type T for a class ``` abstrac kotlinlang #announcements

juliocbcotta

05/14/2018, 2:57 PM

Hi, how can I access a generic type T for a class ?

abstract class TestCase<T : Activity>() {
    val classz = (javaClass
            .genericSuperclass as ParameterizedType).getActualTypeArguments()[0] as Class<T>
    @Rule
    @JvmField
    val rule = IntentsTestRule(classz, false, false)
	}

This seems to work to

open FooTestCase: TestCase<ActivityA>

, but not to

BarTestCase: FooTestCase

Andreas Sinz

05/14/2018, 2:58 PM

what exactly doesn't work?

05/14/2018, 2:58 PM

You need to walk up the superclass tree until you find the

TestCase

class and then grab the

genericSuperclass

juliocbcotta

05/14/2018, 2:58 PM

java.lang.ClassCastException: java.lang.Class cannot be cast to java.lang.reflect.ParameterizedType

05/14/2018, 2:58 PM

Because the superclass of

BarTestCase

FooTestCase

, which is not parameterized

juliocbcotta

05/14/2018, 2:58 PM

Is there a generic way to get that T value?

05/14/2018, 2:59 PM

You have to loop until you find the class you need.

You could use Guava's TypeToken for an existing implementation.

juliocbcotta

05/14/2018, 3:00 PM

ok, I thought maybe Kotlin could have something to make it easier. Thanks