title: Error: Cannot find symbol variable
body: <p>I watched a tutorial from this guy:<br>
  <a href="https://www.youtube.com/watch?v=-SUvA1fXaKw" rel="nofollow noreferrer">https://www.youtube.com/watch?v=-SUvA1fXaKw</a></p>
  
  <p>At the end (about 9:55) he wrote down: </p>
  
  <pre><code>if(fragment != null) {
          FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
          ft.replace(R.id.content_main, fragment);
          ft.commit();
  </code></pre>
  
  <p>I renamed my content_main in activity_main_menu1_start_seite and I thought I could just replace the content_main with activity_main_menu1_start_seite, but then it says "cannot find Symbol variable activity_main_menu1_start_seite"</p>
  
  <p>Maybe you Need my whole Code.<br>
  I marked you the error as the Blockquote.<br>
  Sorry for any issues (I am new to this site) </p>
  
  <pre><code>package com.d_and_d_studios.test3;
  import android.Manifest;
  import android.app.Fragment;
  import android.content.Intent;
  import android.content.pm.PackageManager;
  import android.graphics.Color;
  import android.os.Bundle;
  import android.support.design.widget.NavigationView;
  import android.support.v4.app.FragmentTransaction;
  import android.support.v4.view.GravityCompat;
  import android.support.v4.widget.DrawerLayout;
  import android.support.v7.app.ActionBarDrawerToggle;
  import android.support.v7.app.AppCompatActivity;
  import android.support.v7.widget.Toolbar;
  import android.view.Menu;
  import android.view.MenuItem;
  import android.view.View;
  import android.widget.TextView;
  import android.widget.Toast;
  
  import at.markushi.ui.CircleButton;
  
  public class MainActivity extends AppCompatActivity
          implements NavigationView.OnNavigationItemSelectedListener {
  
     CircleButton btn;
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main_drawer);
          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.addDrawerListener(toggle);
          toggle.syncState();
  
          NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
          navigationView.setNavigationItemSelectedListener(this);
  
          btn = (CircleButton) findViewById(R.id.circleButton);
      }
  
      @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;
      }
  
      //Brauche ich vielleicht doch noch irgendwann!
      //@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);
      //}
  
      private void displaySelectedScreen(int id) {
          Fragment fragment = null;
  
          switch (id) {
              case R.id.nav_powersavingmode:
                  fragment = new Menu_2_Energiesparmodus();
                  break;
              case R.id.nav_feedback:
                  fragment = new Menu_3_Bewerte_die_App();
                  break;
              case R.id.nav_send:
                  fragment = new Menu_4_Teile_uns_Fehler_mit();
  
          }
  </code></pre>
  
  <blockquote>
    <p>if(fragment != null) {
                    FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
                    ft.replace(R.id.activity_main_menu1_start_seite, fragment);
                    ft.commit();
                }</p>
  </blockquote>
  
  <pre><code>        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
          drawer.closeDrawer(GravityCompat.START);
      }
  
  
      @SuppressWarnings("StatementWithEmptyBody")
      @Override
      public boolean onNavigationItemSelected(MenuItem item) {
          // Handle navigation view item clicks here.
          int id = item.getItemId();
  
          if (id == R.id.nav_powersavingmode) {
              // Handle the camera action
          } else if (id == R.id.nav_feedback) {
  
          } else if (id == R.id.nav_send) {
  
          }
  
          displaySelectedScreen(id);
          return true;
      }
  }
  </code></pre>
  
  <hr>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      xmlns:tools="http://schemas.android.com/tools"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:background="@color/backgroundcolor"
      app:layout_behavior="@string/appbar_scrolling_view_behavior"
      tools:context="com.d_and_d_studios.test3.MainActivity"
      tools:showIn="@layout/toolbar_main"&gt;
  
      &lt;at.markushi.ui.CircleButton
          android:id="@+id/circleButton"
          android:layout_width="116dp"
          android:layout_height="116dp"
          android:layout_centerInParent="true"
          android:src="@drawable/ic_power_settings_new_black_24dp"
          app:cb_color="#000"
          app:cb_pressedRingWidth="20dp"
  
          tools:layout_editor_absoluteY="178dp"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintRight_toRightOf="parent" /&gt;
  
      &lt;TextView
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:text="@string/menu1_text1"
          android:fontFamily="sans-serif"
          android:textColor="@color/colorPrimary"
          app:layout_constraintBottom_toBottomOf="parent"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintRight_toRightOf="parent"
          app:layout_constraintTop_toTopOf="parent"
          app:layout_constraintHorizontal_bias="0.0"
          app:layout_constraintVertical_bias="0.23" /&gt;
  
  &lt;/android.support.constraint.ConstraintLayout&gt;
  </code></pre>