Android Things kotlin example, see BoardDefaults here: https://github.com/androidthings/sample-button/blob/master/app/src/main/java/com/example/androidthings/button/BoardDefaults.java

ButtonActivity.kt

package fr.xebia.androidthingskotlin

import android.app.Activity
import android.os.Bundle
import android.view.KeyEvent
import com.google.android.things.contrib.driver.button.Button
import com.google.android.things.contrib.driver.button.ButtonInputDriver
import com.google.android.things.pio.Gpio
import com.google.android.things.pio.PeripheralManagerService

class ButtonActivity : Activity() {

    private lateinit var ledGpio: Gpio
    private lateinit var buttonInputDriver: ButtonInputDriver

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        val pioService = PeripheralManagerService()
        ledGpio = pioService.openGpio(BoardDefaults.gpioForLED)
        ledGpio.setDirection(Gpio.DIRECTION_OUT_INITIALLY_LOW)
        buttonInputDriver = ButtonInputDriver(
                BoardDefaults.gpioForButton,
                Button.LogicState.PRESSED_WHEN_LOW,
                KeyEvent.KEYCODE_SPACE)
        buttonInputDriver.register()
    }

    override fun onKeyDown(keyCode: Int, event: KeyEvent): Boolean {
        when (keyCode) {
            KeyEvent.KEYCODE_SPACE -> {
                setLedValue(true)
                return true
            }
            else -> return super.onKeyDown(keyCode, event)
        }
    }

    override fun onKeyUp(keyCode: Int, event: KeyEvent): Boolean {
        when (keyCode) {
            KeyEvent.KEYCODE_SPACE -> {
                setLedValue(false)
                return true
            }
            else -> return super.onKeyUp(keyCode, event)
        }
    }

    private fun setLedValue(value: Boolean) {
        ledGpio.value = value
    }

    override fun onDestroy() {
        super.onDestroy()

        buttonInputDriver.unregister()
        buttonInputDriver.close()

        ledGpio.close()
    }
}