private CommonDropAdapterAssistant getAssistant( CommonDropAdapterDescriptor descriptor) { CommonDropAdapterAssistant asst = (CommonDropAdapterAssistant) dropAssistants .get(descriptor); if (asst != null) { return asst; } synchronized (dropAssistants) { asst = (CommonDropAdapterAssistant) dropAssistants.get(descriptor); if (asst == null) { dropAssistants.put(descriptor, (asst = descriptor .createDropAssistant())); asst.init(contentService); } } return asst; }