MainActivity

package com.test.myapplication

import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import android.util.Log
import kotlinx.android.synthetic.main.activity_main.*

class MainActivity : AppCompatActivity() {

    private val TAG = MainActivity::class.java.simpleName

    private var savedKey = "Halo"

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)


        if (savedInstanceState != null) {
            Log.d(TAG, "onCreate() Restoring previous state");
            /* restore state */
            savedKey = savedInstanceState.getString("savedKey")
        } else {
            Log.d(TAG, "onCreate() No saved state available");
            /* initialize app */
        }

        button.setOnClickListener {
            Log.e("test", "klik")
        }
    }

    override fun onRestoreInstanceState(savedInstanceState: Bundle?) {
        if (savedInstanceState != null) {
            Log.d("savedKey", savedInstanceState.getString("savedKey"));
            /* restore state */
        } else {
            Log.d(TAG, "onCreate() No saved state available");
            /* initialize app */
        }
    }

    override fun onSaveInstanceState(outState: Bundle?) {

        outState?.run {
            putString("savedKey", savedKey)
        }

        super.onSaveInstanceState(outState)
    }
}