如何使用 DropDownPreference 更改主题

Question

I want to use a DropDownPreference for my settings page but despite looking all over the internet, there doesn't seem to be any decent tutorial on how to do this. Does anyone know what should go in the onPreferenceChange method? I previously used a RadioButton but now want to use a DropDownPreference for easier implementation and maintenance.

Activity

class SettingsActivity : AppCompatActivity(), FragmentSettings.PreferenceXchangeListener {
    private var mCurrentValue: Boolean = false // False is the default value

    override fun onCreate(savedInstanceState: Bundle?) {
        val mSharedPreferences = PreferenceManager.getDefaultSharedPreferences(this)
        mCurrentValue = mSharedPreferences.getBoolean("preference_dark", false)

        if (mCurrentValue) {
            setTheme(R.style.MyDarkSettingsTheme)
        } else {
            setTheme(R.style.MyLightSettingsTheme)
        }

        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_settings)


        val viewllSettingsContainer = settings_container
        val root = viewllSettingsContainer.rootView


        if (mCurrentValue) {
            root.setBackgroundColor(Color.BLACK)
        } else {
            root.setBackgroundColor(Color.WHITE)
        }

        val settingsFragment = FragmentSettings()
        supportFragmentManager
            .beginTransaction()
            .replace(R.id.settings_container, settingsFragment)
            .commit()
    }


    override fun onXchange(value:Boolean) {
        when {
            mCurrentValue != value -> {
                mCurrentValue = value
                recreate()
            }
        }
    }

    override fun onOptionsItemSelected(item: MenuItem): Boolean {
        return when (item.itemId) {
            android.R.id.home -> {
                val intent = parentActivityIntent
                intent?.addFlags(Intent.FLAG_ACTIVITY_NO_ANIMATION)
                onBackPressed()
                true
            }

            else ->
                super.onOptionsItemSelected(item)
        }
    }
}

Fragment

class SettingsFragment : PreferenceFragmentCompat(), Preference.OnPreferenceChangeListener,
    Preference.OnPreferenceClickListener {
    override fun onCreatePreferences(savedInstanceState: Bundle?, rootKey: String?) {
        addPreferencesFromResource(R.xml.app_preferences)
    }
}

Answer 1

I think you're over-complicating it. There is no need to involve the fragment in listening to changes to a preference it won't be handling and passing that back to the activity. You can register a preference change listener for all preferences in your Activity and respond accordingly there.

class SettingsActivity : AppCompatActivity(), 
    SharedPreferences.OnSharedPreferenceChangeListener {

    override fun onCreate(savedInstanceState: Bundle?) {
        val sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this)
        sharedPreferences.registerOnSharedPreferenceChangeListener(this)
        //...
    }

    override fun onDestroy() {
        val sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this)
        sharedPreferences.unregisterOnSharedPreferenceChangeListener(this)
        //...
        super.onDestroy()
    }

    override fun onSharedPreferenceChanged(_: SharedPreferences, key: String) {
        when (key){
            "preference_dark" -> recreate()
        }
    }
}