![]() It’s not big, it’s not complicated, but the potential it has can be the difference between a good or a bad application… and a crowded zoo. class AnimalDataSource : ItemKeyedDataSource () In the init method we subscribe to the dataChanges, and if it happens we invalidate. The getKey(…) returns the key of an item, so we can find it in the list.Īlso, this is a DataSource, so this must be invalidated if the database changes. The loadAfter(…) and loadBefore(…) loads a give number of items starting/ending at a key. The loadInitial(…) function triggers a callback (LoadInitialCallback) with the first few list items, depending on the requestedLoadSize. Animalĭata class, contains two strings: name, description. So, how did I use all this to implement my animal dictionary?īelow you can see the classes I’ve created with a brief behaviour description.Īll classes function according to the aforementioned. Note that the PagedList and the DataSource travel together. If the database changes, we invalidate the current DataSource and create a new DataSource which loads the requested data into the proper position of a new PagedList, and then passes it to the adapter. (The PositionalDataSource can show placeholders while the data is loading.) Scrolling the PagedList will trigger the DataSource, thus additional pages will load. Animation will occur and the list will be visible in the RecyclerView. Then, trough the ViewModel this Paged Data will be added (submitted) to the PagedListAdapter. When the LiveData is observed the Factory will create a new DataSource and load the requested subset of data into a PagedList. RecyclerView – the View responsible for visualisationĪfter the Application has started, the LivePagedListBuilder.build() function will be called and a LiveData will be created.PagedListAdapter – Contains and manages the LiveDatas. ![]() ViewModel – Link between UI and DataSources.DataProvide – Creates LiveData – s with the given configuration and DataFactory, caches data.DataSourceFactory – Provides DataSources.If the database changes, this must be invalidated (cache is invalid) Data – “Animals, with name with description”.Using this we can retrieve “pages”, subsets of a list, starting or ending at a given key. In this post, we will focus on the ItemKeyedDataSource. The PagedListAdapter comes with different kinds of DataSources (PositionalDataSource, ItemKeyedDataSource, PageKeyedDataSource) for different uses. With the new Jetpack library, we can load the subset that is currently visible to the user, and no more. #Firebase private cache fullFurthermore, if I move this database to cloud storage and add pictures to it, I’ll have to download around 7.7GB of data.Ī few years ago, the DiffUtil class tried to solve this by loading only the modified items into the adapter, thus making the process faster, but we still had to have the full list to compare it to the modified items. ![]() #Firebase private cache updateEvery time I update the name of a single animal, I must load 7.7M items into the adapter. After a quick research, 8 hours of coding and 4 liters of coffee, I manage to create my list that contains 7.7 million Animals. I have a list, containing all the currently living animal species, each has a name and a description. RecyclerViews and their Adapters are well known ways of displaying lists of data, but they are not optimal, because they load entire lists into themselves, and upon change, they simply reload the full list (using notifyDataSetChanged). ![]()
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