title: Cardview doesn't have any affect on items
body: <p>I'm trying to make my RecyclerView prettier, so I added a CardView. However, I don't see any changes when I ran the app, the UI looks like as if there's no CardView at all - there is not separation between the items. Can you please suggest what's wrong with my code here?</p>
  
  <p>This is my list_item.xml:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;android.support.v7.widget.CardView xmlns:card_view="http://schemas.android.com/apk/res-auto"
      xmlns:android="http://schemas.android.com/apk/res/android"
      android:id="@+id/card_view"
      android:layout_gravity="center"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      card_view:cardCornerRadius="4dp"
      card_view:cardElevation="6dp"&gt;
  
      &lt;RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          xmlns:app="http://schemas.android.com/apk/res-auto"&gt;
  
          &lt;android.support.v7.widget.AppCompatTextView
              android:id="@+id/link_title"
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:textSize="18sp"
              android:padding="1dp"
              android:layout_marginBottom="10dp"
              android:layout_marginStart="10dp"
              android:text="@string/title_place_holder"/&gt;
  
          &lt;LinearLayout
              android:layout_below="@id/link_title"
              android:layout_width="match_parent"
              android:layout_height="wrap_content"
              android:orientation="horizontal"
              &gt;
  
              &lt;android.support.v7.widget.AppCompatImageView
                  android:id="@+id/link_img"
                  android:layout_width="wrap_content"
                  android:layout_height="wrap_content"
                  android:layout_marginStart="10dp"
                  android:layout_marginEnd="10dp"
                  android:layout_gravity="center"
                  app:srcCompat="@drawable/ic_launcher_background"/&gt;
  
              &lt;android.support.v7.widget.AppCompatTextView
                  android:id="@+id/link_summary"
                  android:layout_width="wrap_content"
                  android:layout_height="wrap_content"
                  android:layout_gravity="center"
                  android:textSize="15sp"
                  android:padding="1dp"
                  android:text="@string/summary_place_holder"/&gt;
  
          &lt;/LinearLayout&gt;
  
      &lt;/RelativeLayout&gt;
  
  &lt;/android.support.v7.widget.CardView&gt;
  </code></pre>
  
  <p>This is how I initialize my RecylerView:</p>
  
  <pre><code>    protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
  
          mRecyclerView = (RecyclerView)findViewById(R.id.recyclerView);
  
          mAdapter = new PostsAdapter(mPostList);
          RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(getApplicationContext());
          mRecyclerView.setLayoutManager(layoutManager);
          mRecyclerView.setAdapter(mAdapter);
  
          preparePostData();
      }
  </code></pre>