title: Error: Error parsing XML: unbound prefix in XML
body: <p>I am trying to use a cardview in my project, but while I am creating my XML file for my cardview, I keep getting the error </p>
  
  <blockquote>
    <p>error: Error parsing XML: unbound prefix</p>
  </blockquote>
  
  <p>but if I take out my cardview widget, it works. I looked at other questions and tried their responses but it isn't working. Does anyone see what is wrong with my code?</p>
  
  <pre><code> &lt;?xml version="1.0" encoding="utf-8"?&gt;
   &lt;LinearLayout 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"
       android:orientation="horizontal" &gt;
  
       &lt;android.support.v7.widget.CardView
           android:layout_width="match_parent"
           android:layout_height="wrap_content"
           android:layout_margin="8dp"
           card_view:cardCornerRadius="2dp" &gt;
       &lt;/android.support.v7.widget.CardView&gt;
  
   &lt;/LinearLayout&gt;
  </code></pre>