title: android espresso webview access element in iframe
body: <p>This time I try to use espresso to test my app.
  I use webview to open the url and check below html code 
  I face the question that I can`t access the element in iframe.</p>
  
  <pre><code>&lt;html&gt;
    &lt;head&gt;&lt;/head&gt;
    &lt;body&gt;
      &lt;iframe id="mainFrame" src="Address/Default.aspx" scrolling="no" 
      style="border: 0px; width: 100%; height: 432px; position: absolute;"&gt;
        &lt;html&gt;
          &lt;head&gt;&lt;/head&gt;
          &lt;body&gt;
            &lt;button onclick = "one function"&gt;
          &lt;/body&gt;
        &lt;/html&gt;
      &lt;/iframe&gt;
    &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>I copy the XPTH that is <strong>/html/body/button</strong> and code</p>
  
  <pre><code>onWebView().withElement(findElement(Locator.XPATH, "/html/body/button")).perform(webClick());
  </code></pre>
  
  <p>However, I get <strong>Atom evaluation returned null!</strong> and I can not get element.
  Can espresso get element inside iframe? I can get element not in iframe.</p>