Issue with higher order function as a binding adapter

Question

I am running into issues trying to take a function as a parameter in a binding adapter using Kotlin/Android databinding. This example code throws e: error: cannot generate

Answer 1

Use function: Runnable instead of function: () -> Unit.

Android's data-binding compiler generates java code, to which, your kotlin function's signature looks like void testFunction(), as kotlin adapts Unit as void when calling from java.

On the other hand, () -> Unit looks like kotlin.jvm.functions.Function0 which is a function which takes 0 inputs and returns Unit.INSTANCE.

As you can see these two function signatures don't match, and that's why the compilation fails.