title: RelativeLayout cannot be cast to android.support.v7.widget.Toolbar
body: <p>I want to add shadow to ToolBar and I use the following link:
  <a href="https://stackoverflow.com/questions/26575197/no-shadow-by-default-on-toolbar">ToolBar Shadow</a></p>
  
  <p>but running app show me this error in LogCat : </p>
  
  <pre><code>java.lang.ClassCastException: android.widget.RelativeLayout cannot be cast to android.support.v7.widget.Toolbar
  </code></pre>
  
  <p>Toolbar code : </p>
  
  <pre><code>&lt;RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  xmlns:app="http://schemas.android.com/apk/res-auto"
  android:layout_width="match_parent"
  android:layout_height="200dp"&gt;
  
  &lt;android.support.v7.widget.Toolbar
      android:layout_width="match_parent"
      android:layout_height="200dp"
      app:popupTheme="@style/ThemeOverlay.AppCompat.Dark"
      app:theme="@style/MyCustomToolbarTheme"
      android:background="@drawable/main_header"&gt;
  
      &lt;/android.support.v7.widget.Toolbar&gt;
  </code></pre>
  
  <p>MainActivity XML : </p>
  
  <pre><code>&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"
  tools:context=".MainActivity"&gt;
  
  &lt;include
      android:id="@+id/app_bar"
      layout="@layout/app_bar_main"/&gt;
  
  &lt;TextView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_below="@+id/app_bar"
      android:text="ytkbhjk"/&gt;
  </code></pre>
  
  <p>MainActivity Java : </p>
  
  <pre><code>public class MainActivity extends ActionBarActivity {
  
  private Toolbar toolbar;
  
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
  
      toolbar = (Toolbar) findViewById(R.id.app_bar);
      setSupportActionBar(toolbar);
      getSupportActionBar().setDisplayShowHomeEnabled(true);
  }
  </code></pre>
  
  <p>please help me</p>