How to retain selection in multi choice dialog in Android on rotation?

Question

I have a dialog to select more than one days of a week as follows:

class DialogSettingsEnabledDays : DialogFragment() {
    override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {

        return activity.let {

            val selectedDaysValue = BooleanArray(7) { _ -> false }
            val selectedDaysIndex = ArrayList<Int>()

            val daysToIndexMap = mutableMapOf<String, Int>()
            val indexToDaysMap = mutableMapOf<Int, String>()
            val daysArray = resources.getStringArray(R.array.days_medium)
            for (i in 0..6) {
                daysToIndexMap[daysArray[i]] = i
                indexToDaysMap[i] = daysArray[i]
            }

            val prefs = it!!.getSharedPreferences(getString(R.string.shared_prefs_settings), Context.MODE_PRIVATE)
            val selectedDaysString = prefs.getString("enabled_days", getString(R.string.default_enabled_days))
            val selectedDays = selectedDaysString!!.split(", ")

            for (day in selectedDays) {
                selectedDaysValue[daysToIndexMap.getValue(day)] = true
                selectedDaysIndex.add(daysToIndexMap.getValue(day))
            }

            val enabledDaysBuilder = AlertDialog.Builder(it)
            enabledDaysBuilder
                .setTitle(R.string.settings_enabled_days)
                .setMultiChoiceItems(R.array.days_long, selectedDaysValue) { _, which, isChecked ->
                    if (isChecked)
                        selectedDaysIndex.add(which)
                    else if (selectedDaysIndex.contains(which))
                        selectedDaysIndex.remove(Integer.valueOf(which))
                }
                .setPositiveButton(R.string.dialog_ok) { _, _ ->
                    if (selectedDaysIndex.isEmpty()) {
                        Toast.makeText(it, "Select atleast one day !!", Toast.LENGTH_SHORT).show()
                    } else {
                        selectedDaysIndex.sort()
                        val selectedDaysList = mutableListOf<String>()
                        for (i in selectedDaysIndex) {
                            selectedDaysList.add(indexToDaysMap.getValue(i))
                        }
                        val editor = prefs.edit()
                        editor
                            .putString("enabled_days", selectedDaysList.joinToString())
                            .apply()
                        val enabledDays = it.findViewById<LinearLayout>(R.id.settings_enabled_days)
                        enabledDays.findViewById<TextView>(R.id.secondary_text).text = selectedDaysList.joinToString()
                    }
                }
                .setNegativeButton(R.string.dialog_cancel) { _, _ -> /* do nothing */ }

            enabledDaysBuilder.create()
        }
    }
}

And I am calling this dialog in this way from my activity:

findViewById<LinearLayout>(R.id.settings_enabled_days)
    .setOnClickListener {
        DialogSettingsEnabledDays().show(this.supportFragmentManager, null)
}

My problem is that my selection of days resets to default on rotation. By default I mean the selection stored in SharedPreferences, that is selectedDaysValue in .setMultiChoiceItems. Suppose, these are the selected days when the dialog pops up:

Mon, Tue, Wed, Thu, Fri

Now, I change the selection as:

Mon, Tue

But, when I rotate the phone, the selection sets back to default:

Mon, Tue, Wed, Thu, Fri

How can I retain my selection on orientation change? Because in some apps I have seen, the Dialog selection remains same on rotation.

Answer 1

Well, this is the final solution I have made by making changes in the DialogFragment code only:

Changing the scope of data to be stored:

override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
    return activity.let {
        val selectedDaysValue = BooleanArray(7) { _ -> false }
        val selectedDaysIndex = ArrayList<Int>()

to:

private var selectedDaysValue = BooleanArray(7) { _ -> false }
private var selectedDaysIndex = ArrayList<Int>()

override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
    return activity.let {

Storing the data:

override fun onSaveInstanceState(outState: Bundle) {
    outState.putBooleanArray("selected_days_value", this.selectedDaysValue)
    outState.putIntegerArrayList("selected_days_index", this.selectedDaysIndex)
}

And where I read the data as:

val prefs = it!!.getSharedPreferences(getString(R.string.shared_prefs_settings), Context.MODE_PRIVATE)
val selectedDaysString = prefs.getString("enabled_days", getString(R.string.default_enabled_days))
val selectedDays = selectedDaysString!!.split(", ")

for (day in selectedDays) {
    selectedDaysValue[daysToIndexMap.getValue(day)] = true
    selectedDaysIndex.add(daysToIndexMap.getValue(day))
}

to read from saved state as:

val prefs = activity!!.getSharedPreferences(getString(R.string.shared_prefs_settings), Context.MODE_PRIVATE)
if (savedInstanceState == null) {
    val selectedDaysString = prefs.getString("enabled_days", getString(R.string.default_enabled_days))
    val selectedDays = selectedDaysString!!.split(", ")

    for (day in selectedDays) {
        selectedDaysValue[daysToIndexMap.getValue(day)] = true
        selectedDaysIndex.add(daysToIndexMap.getValue(day))
    }
} else {
    with(savedInstanceState) {
        selectedDaysValue = getBooleanArray("selected_days_value")!!
        selectedDaysIndex = getIntegerArrayList("selected_days_index")!!
    }
}