sgallego

val yearInputFilter: InputFilter = object : InputFilter {
        override fun filter(source: CharSequence?, start: Int, end: Int, dest: Spanned?, dStart: Int, dEnd: Int): CharSequence {
            if (source.isNullOrEmpty()) { //Delete. Do nothing.
                return source ?: ""
            } else {

                val p1 = dest?.toString()?.take(dStart) ?: ""
                val p2 = dest?.takeLast(dest.toString().length - dEnd)
                val endString = p1 + source + p2

sgallego

import android.arch.lifecycle.LiveData
import android.content.SharedPreferences

abstract class SharedPreferenceLiveData<T>(val sharedPrefs: SharedPreferences,
                                  val key: String,
                                  val defValue: T) : LiveData<T>() {

  private val preferenceChangeListener = SharedPreferences.OnSharedPreferenceChangeListener { sharedPreferences, key ->
    if (key == this.key) {
      value = getValueFromPreferences(key, defValue)