How to convert lambda function in java to kotlin when there is one method in interface?

Question

I want to set a listener in kotlin. Is there a way we can set it just similar to java lambda function (this::methodName)?

i tried converting it to kotlin automatically but it gives me error InterfaceListener does not have constructors

public class TestActivity {

    private Listener mListener;

    private void init(){
        setListener(this::onDataAdded);
    }

    private void onDataAdded(TestData testData) {

    }

    public void setListener(Listener listener) {
        this.mListener = listener;
    }

    interface Listener{
        void onDataAdded(TestData testData);
    }

    class TestData {
        String data;
    }

}

java to kotlin IDE converstion error message InterfaceListener does not have constructors

class TestActivity {

    private var mListener: Listener? = null

    private fun init() {
        setListener(Listener { this.onDataAdded(it) })
    }

    private fun onDataAdded(testData: TestData) {

    }

    fun setListener(listener: Listener) {
        this.mListener = listener
    }

    internal interface Listener {
        fun onDataAdded(testData: TestData)
    }

    internal inner class TestData {
        var data: String? = null
    }

}

Short answer: no. Extended Answer: stackoverflow.com/a/33610615/2224047 — Nikolai Shevchenko
– Nikolai Shevchenko, Commented Aug 7, 2019 at 4:33

Andrei Tanana · Accepted Answer · 2019-08-07 06:00:59Z

1

You can move your Listener interface to Java file so setListener(Listener { this.onDataAdded(it) }) will work.

Or you can use a function instead of the listener like this:

typealias Listener = (TestActivity.TestData) -> Unit

class TestActivity {
    private var mListener: Listener? = null

    private fun init() {
        setListener(this::onDataAdded)
    }

    private fun onDataAdded(testData: TestData) {

    }

    fun setListener(listener: Listener) {
        this.mListener = listener
    }

    inner class TestData {
        var data: String? = null
    }
}

answered Aug 7, 2019 at 6:00

Andrei Tanana

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