How to use the preferences of my preferences.xml file in my fragments?

I have two packages in my android app: the MainActivity that handles my NavigationDrawer in the first package, and the fragments of the NavigationDrawer in the second package. Now I created a settings_fragment in the second package for some user settings, and a preferences.xml file in res/xml.

My question: How can these fragments get those preferences, and how to save them? There is a checkbox in my settings_fragment.xml, and I want this checkbox to decide between two actions. For example

• checkbox checked: calculate_round()

• checkbox not checked: calculate()

  How do I manage that?

MainActivity.java:

public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.setDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);

        FragmentManager fm = getFragmentManager();
        fm.beginTransaction().replace(R.id.content_frame, new MainFragment()).commit();
    }

    @Override
    public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.

        FragmentManager fm = getFragmentManager();

        int id = item.getItemId();

        if (id == R.id.notenrechner) {
            // Handle the camera action
            fm.beginTransaction().replace(R.id.content_frame, new NotenrechnerFragment()).commit();
        } else if (id == R.id.begriffe) {
            fm.beginTransaction().replace(R.id.content_frame, new BegriffeFragment()).commit();
        } else if (id == R.id.settings) {
            fm.beginTransaction().replace(R.id.content_frame, new SettingsFragment()).commit();
        } else if (id == R.id.teilen) {

        } else if (id == R.id.bewerten) {

        } else if (id == R.id.beenden) {
            fm.beginTransaction().replace(R.id.content_frame, new BeendenFragment()).commit();
        }

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }
}

First of all, you have to save the value of checkbox in SharedPreferences. Add this code to your settings_fragment's just after calling addPreferencesFromResource(),

CheckBoxPreference checkBoxPreference = (CheckBoxPreference) findPreference("key");
checkBoxPreference.setOnPreferenceClickListener(new OnPreferenceClickListener() {
    @Override
    public boolean onPreferenceClick(Preference preference) {
        boolean checked = ((CheckBoxPreference)preference).isChecked();
        SharedPreferences sharedPreferences = getPreferences(Context.MODE_PRIVATE);
        SharedPreferences.Editor editor = sharedPreferences.edit();
        editor.putBoolean("checkboxValue", checked);
        editor.commit();
        return false;
    }
});

Then you can get this value and decide upon the retrieved value,

boolean checked = sharedPreferences.getBoolean("checkboxValue", <defaultvalue>);
if(checked) {
    calculate_round();
} else {
    calculate();
}