title: android picasso clear cache
body: <p>I am using Picasso to show one's portrait, when the protrait is changed, I want to clear this user's cache(or all users' portrait cache), here is my code, and it doesn't work,anyone can help me?</p>
  
  <pre><code>LruCache lruCache = new LruCache(context);
  lruCache.clear();
  Picasso picasso = new Picasso.Builder(context).memoryCache(lruCache).build();
  picasso.load(portraitUrl).resize(50, 50).centerCrop().error(R.drawable.user_portrait).into(portaitView);
  </code></pre>