Issue with higher order function as a binding adapter

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 view binders java.lang.StackOverflowError` when building with no other useful info in the log.

Here is my binding adapter:

@JvmStatic
@BindingAdapter("onDelayedClick")
fun onDelayedClick(view: View, function: () -> Unit) {
// TODO: Do something
}

XML:

<View
android:id="@+id/test_view"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
app:onDelayedClick="@{() -> viewModel.testFunction()}"/>

and method in my ViewModel:

fun testFunction() = Unit

I have been struggling with this for a bit now and nothing I've tried works, so any help is appreciated.

The declaration `() -> Unit` suggests a function which takes no input and returns nothing (`Unit` is the return type in this statement). Your function should look like this:

fun testFunction() = {}

In the [Event Handling](

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) section I came across this line:

In Listener Bindings, only your return value must match the expected return value of the listener (unless it is expecting void)

For more about error :

> cannot generate view binders java.lang.StackOverflowError

read [this](

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) article. hope it will help you!!

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.

Put `apply plugin: 'kotlin-kapt'` in build.gradle

Then you can create Binding Adapter like

@JvmStatic
@BindingAdapter("onDelayedClick")
fun onDelayedClick(view: View, function: () -> Unit) {
// TODO: Do something
}
And XML Like

<View
android:id="@+id/test_view"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
app:onDelayedClick="@{viewModel.testFunction}"/>

And VM Like

val testFunction = {
// TODO: Do something
}