How to fill ListPreference dynamically when onPreferenceClick is triggered?

android, android-preferences

Solution

You are getting the exception because your ListPreference object is not initialized - you either need to set `entries` and `entryValues` attributes in your XML or do it programatically in `onCreate()` or in `onCreatePreferences()` (e.g. when using `androidx.preference.PreferenceFragmentCompat`).

If if you need to change the items in the list dynamically after the initial ListPreference object has been initialized then a `OnPreferenceClickListener` needs to be set on the ListPreference object. Use the key you have specified in the XML to get a handle to the preference.

Since the code to populate the `entries` and `entryValues` arrays will have to be run both in `onCreate()` and in `onPreferenceClick`, it makes sense to extract it to a separate method - `setListPreferenceData()` in order to avoid duplication.

public class SettingsActivity extends PreferenceActivity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        try {
            addPreferencesFromResource(R.xml.settings);
        } catch (Exception e) {

        }

        final ListPreference listPreference = (ListPreference) findPreference("language");

        // THIS IS REQUIRED IF YOU DON'T HAVE 'entries' and 'entryValues' in your XML
        setListPreferenceData(listPreference);

        listPreference.setOnPreferenceClickListener(new OnPreferenceClickListener() {
            @Override
            public boolean onPreferenceClick(Preference preference) {
                    
                setListPreferenceData(listPreference);
                return false;
            }
        });
    }

    protected static void setListPreferenceData(ListPreference lp) {
            CharSequence[] entries = { "English", "French" };
            CharSequence[] entryValues = {"1" , "2"};
            lp.setEntries(entries);
            lp.setDefaultValue("1");
            lp.setEntryValues(entryValues);
    }
}

Here is another example from google's DeskClock app:

Problem

Original source