Tag: getDefaultSharedPreferences

How to make user changes to options within the Settings Fragment affect changes in the app.

In the Activity call a function to setup shared preferences, then create that function. We will also link the shared preference object with the onSharedPreferenceChangeListener using .registerOnSharedPreferenceChangeListener:
@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_xxxxx);
        mTargetView =  findViewById(R.id.activity_xxxxx); // View to be affected by the preference change
        setupSharedPreferences(); // Call custom function to set up preferences
    }

    private void setupSharedPreferences() {
        SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this); // Get a reference to the default shared preferences from the PreferenceManager class
        mTargetView.setShowText(sharedPreferences.getBoolean(getString(R.string.pref_xxxxx), getResources().getBoolean(R.bool.pref_xxxxx_default))); // Get the value of a preference and use it to call a function (in this case, the custom function mTargetView.setShowText) which will change behaviour in the app
        sharedPreferences.registerOnSharedPreferenceChangeListener(this); // We can use 'this' as context as the Activity will implement OnSharedPreferenceChangeListener (see next)
    }

To make sure the Activity implements the change without having to force an onCreate (e.g.rotate device) implement an OnSharedPreferenceChangeListener within the relevant Activity:
public class xxxxxActivity extends AppCompatActivity implements SharedPreferences.OnSharedPreferenceChangeListener {

    @Override
    public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) { // This function already passes us a reference to the sharedPreferences and key, so we don't need to use the PreferenceManager
        if (key.equals(getString(R.string.pref_show_bass_key))) {
            mTargetView.setShowBass(sharedPreferences.getBoolean(key, getResources().getBoolean(R.bool.pref_show_text_default)));
        }
    }
}

Unregister the OnSharedPreferenceChangeListener when the Activity is shut down using .unregisterOnSharedPreferenceChangeListener:
    @Override
    protected void onDestroy() {
        super.onDestroy();
        PreferenceManager.getDefaultSharedPreferences(this).unregisterOnSharedPreferenceChangeListener(this);
    }

ud851-Exercises-student\Lesson06-Visualizer-Preferences\T06.05