I'm trying to edit the text to show the email of the user and add a logout function to a menu item. I used the default Navigation drawer: 
But on trying these two I always get
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
MainActivity.class
public class Options extends AppCompatActivity {
private AppBarConfiguration mAppBarConfiguration;
private Toast backToast;
private long backPressedTime;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_options);
String email2 = LoggedIn.getEmail(this);
Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
DrawerLayout drawer = findViewById(R.id.drawer_layout);
NavigationView navigationView = findViewById(R.id.nav_view);
// Passing each menu ID as a set of Ids because each
// menu should be considered as top level destinations.
mAppBarConfiguration = new AppBarConfiguration.Builder(
R.id.nav_home, R.id.nav_gallery,
R.id.nav_tools)
.setDrawerLayout(drawer)
.build();
NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
NavigationUI.setupActionBarWithNavController(this, navController, mAppBarConfiguration);
NavigationUI.setupWithNavController(navigationView, navController);
/////////////////////////HERE WHERE I EDIT THE TEXTVIEW
TextView txt_email = (TextView) findViewById(R.id.novoemailshow);
txt_email.setText(email2);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.options, menu);
return true;
}
@Override
public boolean onSupportNavigateUp() {
NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
return NavigationUI.navigateUp(navController, mAppBarConfiguration)
|| super.onSupportNavigateUp();
}
/////////////////////////////THE LOGOUT FUNCTION
public void logout(View v) {
LoggedIn.savePassword(null, this);
LoggedIn.saveEmail(null, this);
Intent intent = new Intent(this, MainActivity.class);
startActivity(intent);
finishAffinity();
}
}
nav_header_options.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="@dimen/nav_header_height"
android:background="@drawable/side_nav_bar"
android:gravity="bottom"
android:orientation="vertical"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
android:theme="@style/ThemeOverlay.AppCompat.Dark">
<ImageView
android:id="@+id/imageView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:contentDescription="@string/nav_header_desc"
android:paddingTop="@dimen/nav_header_vertical_spacing"
app:srcCompat="@mipmap/ic_launcher_round" />
<TextView
android:id="@+id/novoemailshow"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="" />
</LinearLayout>
options.xml
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto">
<item
android:id="@+id/action_settings"
android:onClick="logout"
android:orderInCategory="100"
android:title="Logout"
app:showAsAction="never" />
</menu>
I don't get it if MainActivity.class is created to handle all of it, then its created UI views and fragments, where should I be updating? And why are they null?
