Can we pass java method to to kotlin function of type () -> Unit?

Question

I have a method of kotlin like below

 fun initDrawer(drawerView: DrawerView, drawerLayout: DrawerLayout, context: Context, onRefreshClick: ()  -> Unit) {
  }

But when I try to pass initDrawer(drawerView,drawerlayout,this,onRefreshClick()) it gives me an error of required () cannot be applied to(kotlin.Unit)

is it possible to pass methods from java to kotlin.

Answer 1

You have to set return value of your onRefreshClick to Unit:

private Unit onRefreshClick() {
    //do something here
    return Unit.INSTANCE;
}

Then you can call it like this:

initDrawer(drawerView, drawerLayout, this, this::onRefreshClick);

Answer 2

You cannot pass your Java method directly from Java, as the Kotlin parameter expects the method to return Unit.

You can follow the following pattern:

kotlinClass.higherOrderFunction(() -> {functionToPass(); return Unit.INSTANCE;});

where functionToPass() is defined as:

private void functionToPass() {
    // do something
}

In your case:

initDrawer(drawerView, drawerlayout, this, 
  () -> {onRefreshClick(); return Unit.INSTANCE;})