title: Android imageview, scale full screen, and centerCrop
body: <p>How can I have an imageview whose image fills the screen, but maintains its aspect ratio, and fits in the center?</p>
  
  <p>Currently I have large images, larger than phone screen resolution, but I suspect that they will be be letterboxed on devices with higher resolution</p>
  
  <p>What combination of <code>scaleType</code> will do the trick?</p>