Android N change language programmatically

I found really weird bug that is reproduced only on Android N devices.

In tour of my app there is a possibility to change language. Here is the code that changes it.

 public void update(Locale locale) {

    Locale.setDefault(locale);

    Configuration configuration = res.getConfiguration();

    if (BuildUtils.isAtLeast24Api()) {
        LocaleList localeList = new LocaleList(locale);

        LocaleList.setDefault(localeList);
        configuration.setLocales(localeList);
        configuration.setLocale(locale);

    } else if (BuildUtils.isAtLeast17Api()){
        configuration.setLocale(locale);

    } else {
        configuration.locale = locale;
    }

    res.updateConfiguration(configuration, res.getDisplayMetrics());
}

This code works great in activity of my tour ( with recreate() call) but in all next activities all String resources are wrong. Screen rotation fixes it. What can i do with this problem? Should i change locale for Android N differently or it's just system bug?

P.S. Here's what i found. At first start of MainActivity (which is after my tour) Locale.getDefault() is correct but resources are wrong. But in other activities it gives me wrong Locale and wrong resources from this locale. After rotation screen (or perhaps some other configuration change) Locale.getDefault() is correct.

Kuva

Ok. Finally i managed to find a solution.

First you should know that in 25 API Resources.updateConfiguration(...) is deprecated. So instead you can do something like this:

1) You need to create your own ContextWrapper that will override all configuration params in baseContext. For example this is mine ContextWrapper that changes Locale correctly. Pay attention on context.createConfigurationContext(configuration) method.

public class ContextWrapper extends android.content.ContextWrapper {

    public ContextWrapper(Context base) {
        super(base);
    }

    public static ContextWrapper wrap(Context context, Locale newLocale) {
        Resources res = context.getResources();
        Configuration configuration = res.getConfiguration();

        if (BuildUtils.isAtLeast24Api()) {
            configuration.setLocale(newLocale);

            LocaleList localeList = new LocaleList(newLocale);
            LocaleList.setDefault(localeList);
            configuration.setLocales(localeList);

            context = context.createConfigurationContext(configuration);

        } else if (BuildUtils.isAtLeast17Api()) {
            configuration.setLocale(newLocale);
            context = context.createConfigurationContext(configuration);

        } else {
            configuration.locale = newLocale;
            res.updateConfiguration(configuration, res.getDisplayMetrics());
        }

        return new ContextWrapper(context);
    }
}

2) Here's what you should do in your BaseActivity:

@Override
protected void attachBaseContext(Context newBase) {

    Locale newLocale;
    // .. create or get your new Locale object here.

    Context context = ContextWrapper.wrap(newBase, newLocale);
    super.attachBaseContext(context);
}

Note:

Remember to recreate your activity if you want to change Locale in your App somewhere. You can override any configuration you want using this solution.

thyzz

Inspired by various codes (i.e: our Stackoverflow team (shout out people)), I had produced a much simpler version. The ContextWrapper extension is unnecessary.

First let's say you have 2 buttons for 2 languages, EN and KH. In the onClick for the buttons save the language code into SharedPreferences, then call the activity recreate() method.

Example:

@Override
public void onClick(View v) {
    switch(v.getId()) {
        case R.id.btn_lang_en:
            //save "en" to SharedPref here
            break;
        case R.id.btn_lang_kh:
            //save "kh" to SharedPref here
            break;

        default:
        break;
    }
    getActivity().recreate();
}

Then create a static method that returns ContextWrapper, perhaps in a Utils class (coz that's what I did, lul).

public static ContextWrapper changeLang(Context context, String lang_code){
    Locale sysLocale;

    Resources rs = context.getResources();
    Configuration config = rs.getConfiguration();

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
        sysLocale = config.getLocales().get(0);
    } else {
        sysLocale = config.locale;
    }
    if (!lang_code.equals("") && !sysLocale.getLanguage().equals(lang_code)) {
        Locale locale = new Locale(lang_code);
        Locale.setDefault(locale);
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
            config.setLocale(locale);
        } else {
            config.locale = locale;
        }
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
            context = context.createConfigurationContext(config);
        } else {
            context.getResources().updateConfiguration(config, context.getResources().getDisplayMetrics());
        }
    }

    return new ContextWrapper(context);
}

Finally, load the language code from SharedPreferences in ALL ACTIVITY'S attachBaseContext(Context newBase) method.

@Override
protected void attachBaseContext(Context newBase) {
    String lang_code = "en"; //load it from SharedPref
    Context context = Utils.changeLang(newBase, lang_code);
    super.attachBaseContext(context);
}

BONUS: To save palm sweat on keyboard, I created a LangSupportBaseActivity class that extends the Activity and use the last chunk of code there. And I have all other activities extends LangSupportBaseActivity.

Example:

public class LangSupportBaseActivity extends Activity{
    ...blab blab blab so on and so forth lines of neccessary code

    @Override
    protected void attachBaseContext(Context newBase) {
        String lang_code = "en"; //load it from SharedPref
        Context context = Utils.changeLang(newBase, lang_code);
        super.attachBaseContext(context);
    }
}

public class HomeActivity extends LangSupportBaseActivity{
    ...blab blab blab
}

The above answers set me on the right track but left a couple of issues

On android 7 and 9 I could happily change to any language other than the app default. When I changed back to the app default language it showed the last language selected - not surprising as this has overridden the default (although interestingly this wasn't an issue on Android 8!).
For RTL languages it didn't update the layouts to RTL

To fix the first item I stored the default locale on app start.

Note If your default language is set to "en" then locales of "enGB" or "enUS" both need to match the default locale (unless you provide seperate localisations for them). Similarly in the example below if the user's phone locale is arLY (Arabic Libya) then the defLanguage needs to be "ar" not "arLY"

private Locale defLocale = Locale.getDefault();
private Locale locale = Locale.getDefault();
public static myApplication myApp;
public static Resources res;
private static String defLanguage = Locale.getDefault().getLanguage() + Locale.getDefault().getCountry();
private static sLanguage = "en";
private static final Set<String> SUPPORTEDLANGUAGES = new HashSet<>(Arrays.asList(new String[]{"en", "ar", "arEG"})); 

@Override
protected void attachBaseContext(Context base) {
  if (myApp == null) myApp = this;
  if (base == null) super.attachBaseContext(this);
  else super.attachBaseContext(setLocale(base));
}

@Override
public void onCreate() {
  myApp = this;

  if (!SUPPORTEDLANGUAGES.contains(test)) {
    // The default locale (eg enUS) is not in the supported list - lets see if the language is
    if (SUPPORTEDLANGUAGES.contains(defLanguage.substring(0,2))) {
      defLanguage = defLanguage.substring(0,2);
    }
  }
}

private static void setLanguage(String sLang) {
  Configuration baseCfg = myApp.getBaseContext().getResources().getConfiguration();
  if ( sLang.length() > 2 ) {
    String s[] = sLang.split("_");
    myApp.locale = new Locale(s[0],s[1]);
    sLanguage = s[0] + s[1];
  }
  else {
    myApp.locale = new Locale(sLang);
    sLanguage = sLang;
  }
}

public static Context setLocale(Context ctx) {
  Locale.setDefault(myApp.locale);
  Resources tempRes = ctx.getResources();
  Configuration config = tempRes.getConfiguration();

  if (Build.VERSION.SDK_INT >= 24) {
    // If changing to the app default language, set locale to the default locale
    if (sLanguage.equals(myApp.defLanguage)) {
      config.setLocale(myApp.defLocale);
      // restored the default locale as well
      Locale.setDefault(myApp.defLocale);
    }
    else config.setLocale(myApp.locale);

    ctx = ctx.createConfigurationContext(config);

    // update the resources object to point to the current localisation
    res = ctx.getResources();
  } else {
    config.locale = myApp.locale;
    tempRes.updateConfiguration(config, tempRes.getDisplayMetrics());
  }

  return ctx;
}

To fix the RTL issues I extended AppCompatActivity as per Fragments comments in this answer

public class myCompatActivity extends AppCompatActivity {
  @Override
  protected void attachBaseContext(Context base) {
    super.attachBaseContext(myApplication.setLocale(base));
  }

  @Override
  protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (Build.VERSION.SDK_INT >= 17) {
      getWindow().getDecorView().setLayoutDirection(myApplication.isRTL() ?
              View.LAYOUT_DIRECTION_RTL : View.LAYOUT_DIRECTION_LTR);
    }
  }
}

来源：https://stackoverflow.com/questions/39705739/android-n-change-language-programmatically

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