title: Cannot resolve symbol 'R' on every activity
body: <p>I made a little app with an action what can call two fragments. This works absolutely fine even though android studio marks every <strong>findViewById(R.id.Example)</strong> read, what obvisely means there is something wrong. Only the "R" is marked red. But i dont understand what is wrong? Especially when the app works fine and the compilation dont give any errors.</p>
  
  <p>Here is the main activity:</p>
  
  <pre><code>package silverbeach.meintieralter;
  
  import android.app.Fragment;
  import android.app.FragmentTransaction;
  import android.os.Bundle;
  import android.support.design.widget.FloatingActionButton;
  import android.support.design.widget.Snackbar;
  import android.support.v4.app.FragmentActivity;
  import android.support.v7.app.AppCompatActivity;
  import android.support.v7.widget.Toolbar;
  import android.view.View;
  import android.view.Menu;
  import android.view.MenuItem;
  
  public class MainActivity extends AppCompatActivity {
  
      private FragmentOne fragmentOne;
      private FragmentTwo fragmentTwo;
  
  
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
          Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
          setSupportActionBar(toolbar);
  
  
  
          //Fragmente ankündigen
          fragmentOne = (FragmentOne) Fragment.instantiate(this, FragmentOne.class.getName(),null);
          fragmentTwo = (FragmentTwo) Fragment.instantiate(this, FragmentTwo.class.getName(),null);
  
  
          //Fragment 1 wird STANDARTMÄSSIG eingeblendet und ausgeführt
          FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction();
          fragmentTransaction.add(R.id.flFragmentContainer, fragmentOne);
          fragmentTransaction.commit();
  
  
  
      }
  
      @Override
      public boolean onCreateOptionsMenu(Menu menu) {
          // Inflate the menu; this adds items to the action bar if it is present.
          getMenuInflater().inflate(R.menu.menu_main, menu);
          return true;
      }
  
      @Override
      public boolean onOptionsItemSelected(MenuItem item) {
  
          switch (item.getItemId()){
              case R.id.action_one:{
                  FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction();
                  fragmentTransaction.replace(R.id.flFragmentContainer, fragmentOne);
                  fragmentTransaction.commit();
                  break;
              }
              case R.id.action_two:{
                  FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction();
                  fragmentTransaction.replace(R.id.flFragmentContainer, fragmentTwo);
                  fragmentTransaction.commit();
                  break;
              }
              default:{
  
              }
          }
  
          return super.onOptionsItemSelected(item);
      }
  }
  </code></pre>
  
  <p>And here is one of the fragments: </p>
  
  <pre><code>package silverbeach.meintieralter;
  
  import android.app.Fragment;
  import android.content.Context;
  import android.os.Bundle;
  import android.os.Vibrator;
  import android.support.annotation.Nullable;
  import android.support.design.widget.FloatingActionButton;
  import android.support.design.widget.Snackbar;
  import android.view.LayoutInflater;
  import android.view.View;
  import android.view.ViewGroup;
  import android.widget.Button;
  import android.widget.EditText;
  import android.widget.Spinner;
  import android.widget.TextView;
  import android.view.View.OnClickListener;
  
  import static android.content.Context.VIBRATOR_SERVICE;
  
  
  public class FragmentOne extends Fragment {
  
      private TextView out;
      private EditText alter;
      private Spinner s;
      private Button button;
      private FloatingActionButton fab;
  
  
  
      @Override
      public void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
  
  
  
  
      }
  
      @Nullable
      @Override
      public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
  
          View layout = inflater.inflate(R.layout.fragment_one, null);
  
          out = (TextView) layout.findViewById(R.id.out);
          alter = (EditText) layout.findViewById(R.id.altereingabe);
          s = (Spinner) layout.findViewById(R.id.spinner);
          button = (Button) layout.findViewById(R.id.button);
          fab = (FloatingActionButton) layout.findViewById(R.id.fab);
  
  
  
          FloatingActionButton fab = (FloatingActionButton) layout.findViewById(R.id.fab);
          fab.setOnClickListener(new View.OnClickListener()
          {
                                        @Override
                                        public void onClick(View v) {
  
  
  
  
                                            String text = s.getSelectedItem().toString();
                                            int newage = 404;
                                            double doublenewage = 4.04;
                                            double doubleage;
                                            int intage;
                                            doubleage = Double.parseDouble(alter.getText().toString());
                                            intage = (int) doubleage;
  
                                            switch (text) {
                                                case "Katze": {
                                                    switch (intage) {
  
                                                        default:
                                                            Snackbar.make(v, "Leider schon tot.", Snackbar.LENGTH_LONG).show();
                                                            out.setText("Leider schon tot.");
                                                            break;
  
  
                                                    }
                                                    if (intage &lt;= 119)
                                                        Snackbar.make(v, "Du bist eine " + Integer.toString(newage) + " Jahre alte Katze.", Snackbar.LENGTH_LONG).show();
  
                                                    else {
                                                        double deadagecat;
                                                        deadagecat = intage * 0.283;
                                                        long dc = Math.round(deadagecat);
                                                        Snackbar.make(v, "Du bist höchstwahrscheinlich schon tot, aber theoretisch wärst du eine " + dc + "-Jährige Katze.", Snackbar.LENGTH_LONG).show();
  
  
                                                    }
  
  
                                                }break;
                                                case "Pferd": {
                                                    doublenewage = intage / 3.1;
                                                    long longpferdage = Math.round(doublenewage);
                                                    newage = (int) longpferdage;
  
                                                    if (newage &lt; 31)
                                                        Snackbar.make(v, "Du bist ein " + Integer.toString(newage) + " Jahre altes Pferd", Snackbar.LENGTH_LONG).show();
  
                                                    else
                                                        Snackbar.make(v, "Du bist höchstwahrscheinlich schon tot, aber theoretisch wärst du ein " + newage + "-Jähriges Pferd.", Snackbar.LENGTH_LONG).show();
  
                                                }break;
                                                case "Hund": {
                                                    newage = intage / 7;
                                                    if (newage &lt; 15)
                                                        Snackbar.make(v, "Du bist ein " + Integer.toString(newage) + " Jahre alter Hund.", Snackbar.LENGTH_LONG).show();
  
                                                    else
                                                        Snackbar.make(v, "Du bist höchstwahrscheinlich schon tot, aber theoretisch wärst du ein " + newage + "-Jähriger Hund.", Snackbar.LENGTH_LONG).show();
  
  
                                                }break;
                                                case "Meerschweinchen": {
                                                    newage = intage / 12;
                                                    if (newage &lt; 8)
  
                                                        //out.setText("Du bist ein " + Integer.toString(newage) + " Jahre altes Meerie.");
                                                        Snackbar.make(v, "Du bist ein "+Integer.toString(newage)+" Jahre altes Meerie.", Snackbar.LENGTH_LONG).show();
  
  
  
  
  
  
                                                    else{
                                                    Snackbar.make(v, "Du bist höchstwahrscheinlich schon tot, aber theoretisch wärst du ein " + newage + "-Jähriges Meerie.", Snackbar.LENGTH_LONG).show();}
  
  
                                                }break;
  
  
                                            }
  
  
  
                                        }
  
  
                                    });
          // tvText1 = (TextView) layout.findViewById(R.id.tvFragmentOne);
  
  
  
  
  
          return layout;
      }
  
  
  
  
  
      @Override
      public void onActivityCreated(Bundle savedInstanceState) {
          super.onActivityCreated(savedInstanceState);
  
          //tvText1.setText("Ok View 1 wurde geändert.");
  
      }
  }
  </code></pre>