Why does Android Studio Java pages has errors on R.id?

Question

I just started a college project with android studio, and I faced so many errors recently it was ok before!

all the activities.java have errors but XMLs is fine I had one error and I send it to someone and he said he fixed it. that error is gone now but so many other errors appeared.

All the Javas have these same errors (R.id has red underline):

btnMakeCall = findViewById(R.id.support_call_btn);
btnSendEmail = findViewById(R.id.support_send_email_btn);

DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);

MainActivity has these errors also (all are red underlined):

public class MainActivity extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener {

TextSliderView textSliderView;
RelativeLayout relativeLayoutPardakhtGhabz;