Changing locale in MainActivity works, but changing it in Fragment gives Nullpointerexception

Question

I have a ListPreference which I want to use to change the language of my app.

    <ListPreference
        android:key="@string/language_preference"
        android:title="@string/preference_title"
        android:entries="@array/language_array"
        android:entryValues="@array/language_data"
        app:iconSpaceReserved="false" />

I'm using this localization library to help. In my MainActivity I have two functions to change the (currently) two supported languages:

    fun changeLanguageGer() {
        setLanguage("de")
    }

    fun changeLanguageEn() {
        setLanguage("en")
    }

I happen to have a spinner in my MainActivity that I "misused" to check if those methods work: When changing to the according spinner item my app language changes as expected.

But I actually want to make this change in my settings with the ListPreference.

In the SettingsFragment I have the following code:

class SettingsActivity : LocalizationActivity() {

    class SettingsFragment : PreferenceFragmentCompat() {
        override fun onCreatePreferences(savedInstanceState: Bundle?, rootKey: String?) {
            setPreferencesFromResource(R.xml.root_preferences, rootKey)
            ...

            // language
            val listPreference =
                findPreference<Preference>(getString(R.string.language_preference)) as ListPreference?
            listPreference?.setOnPreferenceChangeListener { preference, newValue ->
                if (preference is ListPreference) {
                    val index = preference.findIndexOfValue(newValue.toString())
                    val locale = preference.entryValues[index]
                    if (locale == "de") {
                        Toast.makeText(activity,locale, Toast.LENGTH_LONG).show()
                        MainActivity().changeLanguageGer()
                    }
                    if (locale == "en") {
                        Toast.makeText(activity,locale, Toast.LENGTH_LONG).show()
                        MainActivity().changeLanguageEn()
                    }
                }
                true
            }
        }
    }
}

This gives me the following Nullpointerexception: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.SharedPreferences android.content.Context.getSharedPreferences(java.lang.String, int)' on a null object reference. I added the toast statements to make sure the output I get when clicking on the language I want to change to is correct, which it is (either gives me "de" or "en").

How would I go about debugging this?

Does this answer your question? [What is a NullPointerException, and how do I fix it?](https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — Ehsan msz, Dec 02 '20 at 02:56
I do generally know what a Nullpointerexception is, but I don't know where it is coming from in this case and how I could fix it — Brian, Dec 02 '20 at 02:57
the error log tells you that you are calling `getSharedPreferences()` method on a null reference which is context. make sure you invoke that method when you have context. you have to read about the activity lifecycle and Do Not make an instance of activity like you did for `MainActivity`. — Ehsan msz, Dec 02 '20 at 03:04

Destroyer · Accepted Answer · 2020-12-02T03:07:46.643

1

(activity as SettingsActivity).changeLanguageEn()

Try using this to change the language.

edited Dec 02 '20 at 03:07

answered Dec 02 '20 at 03:02

Destroyer

785
8
20

This results in `java.lang.ClassCastException: com.example.tuner.SettingsActivity cannot be cast to com.example.tuner.MainActivity` - I probably should have specified that the `SettingsFragment` is inside a `SettingsActivity`, will edit my post – Brian Dec 02 '20 at 03:07
Thanks a lot, when putting my two methods for changing the languages into the `SettingsActivity` instead and calling it like that it works! – Brian Dec 02 '20 at 03:10

Changing locale in MainActivity works, but changing it in Fragment gives Nullpointerexception

1 Answers1