@Override
          public void onClick(View v) {
            mPrefetchBitmapButton.setEnabled(false);
            final PrefetchSubscriber subscriber = new PrefetchSubscriber();
            for (Uri uri : mUris) {
              final DataSource<Void> ds =
                  Fresco.getImagePipeline().prefetchToBitmapCache(ImageRequest.fromUri(uri), null);
              ds.subscribe(subscriber, UiThreadImmediateExecutorService.getInstance());
            }
          }
Fragment that illustrates how to prefetch images to disk cache so that they load faster when
finally displayed.
samples/showcase/src/main/java/com/facebook/fresco/samples/showcase/imagepipeline/ImagePipelinePrefetchFragment.java