private void watchListAdd(final ProgressButtonDisposableHandler handler) {
            final WatchListCapability connector = (WatchListCapability) ConnectorFactory.getConnector(cache);
            if (connector.addToWatchlist(cache)) {
                handler.sendTextMessage(MESSAGE_SUCCEEDED, R.string.cachedetails_progress_watch);
            } else {
                handler.sendTextMessage(MESSAGE_FAILED, R.string.err_watchlist_failed);
            }
        }
Add this cache to the watchlist of the user
main/src/main/java/cgeo/geocaching/CacheDetailActivity.java