Updating the Screenlet class for offline mode is straightforward. In the
Screenlet class’s onUserAction method, you’ll change the call to the
Interactor’s start method so that it takes only an event as an argument.
Before doing this, however, you should create an event instance and set its
cache key. A cache key is a value that identifies an entity in the local cache.
This lets you retrieve the entity from the cache for later synchronization with
the server.
In Add Bookmark Screenlet, for example, a bookmark’s URL makes a good cache key.
To support offline mode, the onUserAction method in AddBookmarkScreenlet
creates a new BookmarkEvent instance with a bookmark’s data and then uses the
setCacheKey method to set the bookmark’s URL as the event’s cache key. The
Interactor’s start method takes this event as its argument:
BookmarkEvent event = new BookmarkEvent(url, title, folderId);
event.setCacheKey(url);
interactor.start(event);
Note that you don’t have to set a cache key to use offline mode. Instead, you
can pass the event to the start method without calling setCacheKey. However,
this means that you’ll only be able to access the most recent entity in the
cache.
That’s it! Your write Screenlet now supports offline mode. There’s one more detail to keep in mind, however, when using the Screenlet: syncing the cache with the server. You’ll learn about this next.