Question

I’m trying to use SharedPreferences to store a preference, then change the default checked state of the menu item based on the SharedPreference. But it does not seem to be working. The menu choice stays until the app is closed. When I reload the app, the setting is back to the default, instead of the new SharedPreference setting.

public class MainActivity extends Activity {

boolean prefs = true;
String FILENAME = "settings";
String string;

public static final String LOG_TAG = "dbryant423";
public static final String PREFS_NAME = "settings";

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Log.v(LOG_TAG, "prefs value: " +prefs);

 }

public boolean onCreateOptionsMenu(Menu menu) {

    getMenuInflater().inflate(R.menu.menu, menu);
    SharedPreferences settings = getSharedPreferences(PREFS_NAME, 0);
    String preference = settings.getString("preference", string);
    if (preference == "us")
        menu.findItem(R.id.menu_us).setChecked(true);
    else if (preference == "metric")
        menu.findItem(R.id.menu_metric).setChecked(true);
    return true; 
}

// called when an item is selected
@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch(item.getItemId()) { // decide which MenuItem was pressed based on it's id
    case R.id.menu_us:
            menuUS();

    case R.id.menu_metric:
            menuMetric();

    }
    return true;
}

@Override
public boolean onPrepareOptionsMenu(Menu menu) {
    super.onPrepareOptionsMenu(menu);
    if (prefs == true)
        menu.findItem(R.id.menu_us).setChecked(true);
    else if (prefs == false)
        menu.findItem(R.id.menu_metric).setChecked(true);
    return true;
}

public void menuUS() {
    prefs = true;
    SharedPreferences settings = getSharedPreferences(PREFS_NAME, 0);
    SharedPreferences.Editor editor = settings.edit();
    editor.putString("preference", "us");
    editor.commit();
}

public void menuMetric() {
    prefs = false;
    SharedPreferences settings = getSharedPreferences(PREFS_NAME, 0);
    SharedPreferences.Editor editor = settings.edit();
    editor.putString("preference", "metric");
    editor.commit();
}

public void calculateCylinder(View v) {
    Intent calculateCylinderUS = new Intent(this, CalculateCylinder.class);
    Intent calculateCylinderMetric = new Intent(this, CalculateCylinderMetric.class);
     Log.v(LOG_TAG, "prefs value: " +prefs);
    if (prefs == true)
        startActivity(calculateCylinderUS);
    else if (prefs == false)
        startActivity(calculateCylinderMetric);
}

Answer 1

Please note that onPrepareOptionsMenu gets called just before the menu is displayed to the user.
Looking at your code you are calling setChecked(true) on R.id.menu_us and R.id.menu_metric based on local variable prefs whose value will always be true whenever the activity is created. So in order to persist these states we must update menu-items based on preference values and not based on values of local variable.

I think you’d rather modify your onPrepareOptionsMenuand onCreateOptionsMenu functions as below and give it a try:

public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.menu, menu);
    return true; 
}

@Override
public boolean onPrepareOptionsMenu(Menu menu) {
    super.onPrepareOptionsMenu(menu);
    SharedPreferences settings = getSharedPreferences(PREFS_NAME, 0);
    String preference = settings.getString("preference", string);
    if (preference == "us")
        menu.findItem(R.id.menu_us).setChecked(true);
    else if (preference == "metric")
        menu.findItem(R.id.menu_metric).setChecked(true);
    return true;
}