Change locale programmatically in Kotlin

Question

I had some codes for change locale programmatically in Java. But when my application migrated to Kotlin, I can't change locale any more.

For example this code in Java worked very good :

public static final void setAppLocale(String language, Activity activity) {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
        Resources resources = activity.getResources();
        Configuration configuration = resources.getConfiguration();
        configuration.setLocale(new Locale(language));
        activity.getApplicationContext().createConfigurationContext(configuration);
    } else {
        Locale locale = new Locale(language);
        Locale.setDefault(locale);
        Configuration config = activity.getResources().getConfiguration();
        config.locale = locale;
        activity.getResources().updateConfiguration(config,
                activity.getResources().getDisplayMetrics());
    }
}

I tried many codes in Kotlin but non of them worked for me. This is my last try:

fun changeLanguage(context: Context, language : String) {
    val locale = Locale(language)
    Locale.setDefault(locale)

    val config = context.resources.configuration
    config.setLocale(locale)
    context.createConfigurationContext(config)
    context.resources.updateConfiguration(config, context.resources.displayMetrics)
}

How can I change application's local in Kotlin? Old codes that were written in Java did not work in Kotlin application.

Answer 1

Create a Context helper class let's say

class ApplicationLanguageHelper(base: Context) : ContextThemeWrapper(base, R.style.AppTheme) {
companion object {

    fun wrap(context: Context, language: String): ContextThemeWrapper {
        var context = context
        val config = context.resources.configuration
        if (language != "") {
            val locale = Locale(language)
            Locale.setDefault(locale)
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
                setSystemLocale(config, locale)
            } else {
                setSystemLocaleLegacy(config, locale)
            }
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
                config.setLayoutDirection(locale)
                context = context.createConfigurationContext(config)
            } else {
                context.resources.updateConfiguration(config, context.resources.displayMetrics)
            }
        }
        return ApplicationLanguageHelper(context)
    }

    @SuppressWarnings("deprecation")
    fun setSystemLocaleLegacy(config: Configuration, locale: Locale) {
        config.locale = locale
    }

    @TargetApi(Build.VERSION_CODES.N)
    fun setSystemLocale(config: Configuration, locale: Locale) {
        config.setLocale(locale)
    }
}

}

And in your Activity you can override attachBaseContext

    override fun attachBaseContext(newBase: Context?) {
    super.attachBaseContext(ApplicationLanguageHelper.wrap(newBase!!, "fa"))
}

To Change the language you can use a Spinner or any other preferred way, to call the following method OnClick

   private fun changeApplicationLanguage(language:String){
    val sharedPreferencesEditor = sharedPreferences.edit()
    when (language) {
        ENGLISH -> sharedPreferencesEditor?.putString(SELECTED_LANGUAGE, ENGLISH)
        PERSIAN -> sharedPreferencesEditor?.putString(SELECTED_LANGUAGE, PERSIAN)
        PASHTO -> sharedPreferencesEditor?.putString(SELECTED_LANGUAGE, PASHTO)
    }
    sharedPreferencesEditor.putBoolean(LANGUAGE_IS_SELECTED, true)
    sharedPreferencesEditor?.apply()
    recreate()
}

make sure you define sharedPreferences and also SELECTED_LANGUAGE , ENGLISH etc, consts

const val SELECTED_LANGUAGE = "language"
const val ENGLISH = "en"
const val PERSIAN = "fa"
const val PASHTO = "ps"

 private lateinit var sharedPreferences: SharedPreferences

and also initialize sharedPreferences in onCreate method after setContent

sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this@Your_Activity_Name)

also Override the base context by adding the following code

 // Overwrite the context
override fun attachBaseContext(newBase: Context?) {
    sharedPreferences = PreferenceManager.getDefaultSharedPreferences(newBase)
    val lang = sharedPreferences.getString(SELECTED_LANGUAGE, "en")
    super.attachBaseContext(ApplicationLanguageHelper.wrap(newBase!!, lang!!))
}

I am sure this method is not an optimal solution, but, this might help

Answer 2

Try this

fun setAppLocale(languageFromPreference: String?, context: Context) 
{
    
    if (languageFromPreference != null) {

        val resources: Resources = context.resources
        val dm: DisplayMetrics = resources.displayMetrics
        val config: Configuration = resources.configuration
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
            config.setLocale(Locale(languageFromPreference.toLowerCase(Locale.ROOT)))
        } else {
            config.setLocale(Locale(languageFromPreference.toLowerCase(Locale.ROOT)))
        }
        resources.updateConfiguration(config, dm)
    }
}

You can set the App Locale within activities by accessing this function from the activities

    ..
    super.onCreate(savedInstanceState)
    setAppLocale(pref.getLanguageFromPreference().toString(), this)
    setContentView(R.layout.activity_main)
    ...

pref.getLanguageFromPreference() returns the langugae string (For example : "en")