title: Picasso doesn't seem to use the memoryCache I give it
body: <p>In a project I'm working on (named Boxsetter) I'm trying to get Picasso to use a disk cache I've created (BoxsetterImageCache, implementing the Cache interface):</p>
  
  <pre><code>new Picasso.Builder(activity)
     .memoryCache(new BoxsetterImageCache(activity))
     .build()
     .with(activity)
     .load(be.getImg())
     .placeholder(R.drawable.boxsetter2)
     .into(imageView);
  </code></pre>
  
  <p>Through logging I can see the BoxsetterImageCache instance get created. However, no -get- or -set-, or any other method, is called on the BoxsetterImageCache instance after that (which I can tell through the absence of copious logs firing, and no files being created).</p>
  
  <p>The rest of Picasso is working fine: the placeholder is being placed in the ImageView and then happily replaced by images accessed over http. However, it doesn't seem to be calling methods on the cache.</p>
  
  <p>Any ideas as to why that might be? Is there something wrong with this implementation?</p>
  
  <p>Cheers</p>
  
  <p>Nic</p>
  
  <p>BoxsetterImageCache:</p>
  
  <pre><code>package com.boxsetter;
  
  import android.graphics.Bitmap;
  import android.graphics.BitmapFactory;
  import android.util.Log;
  
  import com.squareup.picasso.Cache;
  
  import java.io.File;
  import java.io.FileInputStream;
  import java.io.FileNotFoundException;
  import java.io.FileOutputStream;
  
  /**
   * Created by nic.ford on 27/04/15.
   */
  public class BoxsetterImageCache implements Cache {
  
      private String filesDir;
  
      public BoxsetterImageCache(BoxsetterActivity ba) {
          Log.d("BSBIC", "BIC created"); // THIS LOG IS SEEN
          this.filesDir = ba.getExternalFilesDir(null).getAbsolutePath();
      }
  
      @Override
      public Bitmap get(String key) {
          File file = new File(filesDir + "/bmps/" + key);
  
          // THIS LOG IS NEVER SEEN
          Log.d("BSBIC", "get() File on path: " + file.getAbsolutePath());
  
          if (file.exists()) {
              try {
                  return BitmapFactory.decodeStream(new FileInputStream(file));
              } catch (FileNotFoundException e) {
                  e.printStackTrace();
              }
          }
          return null;
      }
  
      @Override
      public void set(String key, Bitmap bitmap) {
          File file = new File(filesDir + "/bmps/" + key);
  
          // THIS LOG IS NEVER SEEN
          Log.d("BSBIC", "set() File on path: " + file.getAbsolutePath());
  
          try {
              bitmap.compress(Bitmap.CompressFormat.PNG, 100, new FileOutputStream(file));
          } catch (FileNotFoundException e) {
              e.printStackTrace();
          }
      }
  
      @Override
      public int size() {
          File dir = new File(filesDir + "/bmps/");
  
          // THIS LOG IS NEVER SEEN
          Log.d("BSBIC", "size() File on path: " + dir.getAbsolutePath());
  
          int len = 0;
  
          for (File file : dir.listFiles()) {
              len += file.length();
          }
  
          return len;
      }
  
      @Override
      public int maxSize() {
          File file = new File(filesDir + "/bmps/");
  
          // THIS LOG IS NEVER SEEN
          Log.d("BSBIC", "maxSize() File on path: " + file.getAbsolutePath());
  
          return (int)file.getFreeSpace();
      }
  
      @Override
      public void clear() {
          File dir = new File(filesDir + "/bmps/");
  
          // THIS LOG IS NEVER SEEN
          Log.d("BSBIC", "clear() File on path: " + dir.getAbsolutePath());
  
          for (File file : dir.listFiles()) {
              if (file.exists()) file.delete();
          }
      }
  
      @Override
      public void clearKeyUri(String keyPrefix) {
          File dir = new File(filesDir + "/bmps/");
  
          // THIS LOG IS NEVER SEEN
          Log.d("BSBIC", "clearKeyUri() File on path: " + dir.getAbsolutePath());
  
          for (File file : dir.listFiles()) {
              if (file.getName().startsWith(keyPrefix)) file.delete();
          }
      }
  }
  </code></pre>