Writting to external storage (SD card) for Android (SDK 23) in Kotlin 1.0.3.

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    package="xxx">

    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

    ...
</manifest>

MainActivity.kt

package xxx

import android.Manifest
import android.content.Intent
import android.content.pm.PackageManager
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.support.v4.app.ActivityCompat
import android.support.v4.content.ContextCompat

class MainActivity : AppCompatActivity() {

    companion object {
        const val REQUEST_PERMISSION = 1
    }

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

    override fun onStart() {
        super.onStart()
        if (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(this, arrayOf(Manifest.permission.WRITE_EXTERNAL_STORAGE), REQUEST_PERMISSION)
        } else {
            write()
        }
    }

    override fun onRequestPermissionsResult(requestCode: Int, permissions: Array<out String>, grantResults: IntArray) {
        when (requestCode) {
            REQUEST_PERMISSION -> if (grantResults.size > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                write()
            }
        }
    }

    private fun write() {
        val dir = "${Environment.getExternalStorageDirectory()}/$packageName"
        File(dir).mkdirs()
        val file = "%1\$tY%1\$tm%1\$td%1\$tH%1\$tM%1\$tS.log".format(Date())
        File("$dir/$file").printWriter().use { 
            it.println("text")
        }
    }
}