title: System.IO.File does not contain a definition for ReadAllBytes
body: <p>I read image bytes with <code>File.ReadAllBytes()</code> when I develop an Android application with xamarin.forms. The code works well in debug mode. However, it throws an error</p>
  <blockquote>
  <p>System.IO.File does not contain a definition for ReadAllBytes</p>
  </blockquote>
  <p>in release mode. I wonder why this happened? Can I fix it by changing some settings for visual studio? Or it is ok that I use other way to read image byte.</p>