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Chapter 13. Exploring Content Providers > A “Network MVC”
13.2. A “Network MVC”
We like to think of the second pattern as a networked form of MVC, where the content provider itself pulls data from the network and then pumps it into the regular Android MVC. We’ll view the content provider as a model of network state—the provider can fulfill data requests with local state, or can retrieve data from the network. With this approach, the Controller and View code should not directly create network requests to access and manage application data. Instead, your application View and Controller should use the ContentResolver API to make data queries through a content provider, which alone should asynchronously load network resources and store the results in a local data cache. Additionally, the provider should always respond quickly to a request by initially avoiding a network invocation that might be needed to fulfill the request by using whatever data is already available in the local database. Executing the request in this manner ensures that the UI thread is blocked for no longer than absolutely necessary, and that the UI has some data to display as soon as possible, thus improving overall snappiness and user satisfaction when using the UI. Here is the provider sequence for querying data, in more detail:
The provider matches the incoming URI and queries local database contents for items that previously matched the query.
Our provider always attempts to obtain the latest state for the query and subsequently spawns an asynchronous REST request to load content from the network. You could make this behavior configurable based on the request.
The provider returns the cursor from the initial local query to the client.
The asynchronous loading thread should decide if data in the provider cache needs to be refreshed; if it does, the provider loads and parses data from the network.
When content arrives from the network, the provider directly inserts each new data item into the database and then notifies clients of the URIs for the new data. Since the insertion is already happening inside the content provider, there is no need to call ContentResolver.insert. Clients holding existing cursors that contain an older version of data can call Cursor.requery to refresh their data.
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