I'm converting a project in Java to Kotlin and I'm surprise that interface made the code heavier in Kotlin than in Java.
Example: I want to set the onBackPressListener in MainActivity from MyFragment.
File 1: MainActivity, File 2: MyFragment, File 3: OnBackPressedListener (Interface)
File 1 in Java, File 2 in Kotlin, File 3 in Java:
activity.setOnBackPressed { /* Do something */ }
File 1 in Kotlin, File 2 in Kotlin, File 3 in Java:
activity.setOnBackPressed(OnBackPressedListener { /* Do something */ })
File 1 in Kotlin, File 2 in Kotlin, File 3 in Kotlin:
activity.setOnBackPressed(object: OnBackPressedListener {
override fun onBackPressed() {
/* Do something */
}
})
Is it possible to have the 3 files in Kotlin and use lambda to set the listener ? (This is so frustrating to get more code in Kotlin..)
Thanks
The lambda version works only when kotlin interop with java because SAM Conversions, see the official documents.
Also note that this feature works only for Java interop; since Kotlin has proper function types, automatic conversion of functions into implementations of Kotlin interfaces is unnecessary and therefore unsupported.
So if you want use lambda to set the listener with pure kotlin, you can define your listener and setOnBackPressed method like this:
var listener: (() -> Unit)? = null
fun setOnBackPressed(l: () -> Unit) {
listener = l
}
then invoke it by:
listener?.invoke()