title: Toolbar findViewById return null pointer
body: <p>I've already read links about this problem.
  Main solutions were:</p>
  
  <ul>
  <li>disable default action bar. I did....</li>
  <li>put findViewById after setContent. I did...</li>
  <li>include the layout in the main activity layout.xml file. I did..</li>
  </ul>
  
  <p>but still getting null pointer back. I'm getting crazy because also I can't see the toolbar in the preview.</p>
  
  <p><strong>styles.xml</strong></p>
  
  <p>No action bar set.
      </p>
  
  <pre><code>    &lt;!-- Base application theme. --&gt;
      &lt;style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar"&gt;
          &lt;!-- Customize your theme here. --&gt;
          &lt;item name="colorPrimary"&gt;@color/colorPrimary&lt;/item&gt;
          &lt;item name="colorPrimaryDark"&gt;@color/colorPrimaryDark&lt;/item&gt;
          &lt;item name="colorAccent"&gt;@color/colorAccent&lt;/item&gt;
      &lt;/style&gt;
  
  &lt;/resources&gt;
  </code></pre>
  
  <p><strong>my_toolbar.xml</strong></p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;android.support.v7.widget.Toolbar
      xmlns:android="http://schemas.android.com/apk/res/android"
      android:id="@+id/my_toolbar"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:background="@color/colorPrimary"
      android:theme="@style/Theme.AppCompat.DayNight.DarkActionBar"&gt;
  
  &lt;/android.support.v7.widget.Toolbar&gt;
  </code></pre>
  
  <p><strong>activity_maps.xml</strong></p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  
  &lt;RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:tools="http://schemas.android.com/tools"
      android:layout_width="match_parent"
      android:layout_height="match_parent"&gt;
  
      &lt;include
          android:id="@+id/my_toolbar"
          layout="@layout/my_toolbar"/&gt;
  
  
      &lt;!-- Add Google Maps Fragment to the MainActivity --&gt;
      &lt;fragment xmlns:tools="http://schemas.android.com/tools"
          android:id="@+id/map"
          android:name="com.google.android.gms.maps.SupportMapFragment"
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          android:layout_below="@id/my_toolbar"
          tools:context=".MapsActivity" /&gt;
          &lt;!--android:layout_alignParentStart="true"
          android:layout_alignParentTop="true"--&gt;
  
  
  
      &lt;Button
          android:id="@+id/btClear"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_alignParentBottom="true"
          android:layout_centerHorizontal="true"
          android:text="@string/send_screenshot" /&gt;
  
  
  &lt;/RelativeLayout&gt;
  </code></pre>
  
  <p><strong>MapsActivity.java</strong></p>
  
  <p>....  </p>
  
  <pre><code>@Override
          protected void onCreate(Bundle savedInstanceState) {
              super.onCreate(savedInstanceState);
              setContentView(R.layout.activity_maps);
              // Get fused location client
              mFusedLocationClient = LocationServices.getFusedLocationProviderClient(this);
              Toolbar myToolbar = (Toolbar) findViewById(R.id.my_toolbar);
              myToolbar.setTitle("dio porco dio");
              setSupportActionBar(myToolbar);
              // Obtain the SupportMapFragment and get notified when the map is ready to be used.
              SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
                      .findFragmentById(R.id.map);
              mapFragment.getMapAsync(this);
          }
  </code></pre>
  
  <p>....</p>