CS522-Assignment 4 Content Providers Solved

In this assignment, you will extend the chat server app from the previous assignment.  You are required to replace the use of a SQLite database from the previous assignment with a content provider.  Define a single content provider with two tables, visible to the app, and distinguished by their URIs that have the same authority but different content paths.  One table stores the messages that have been received, while the second table stores information about the peers from whom we have received messages. You should define a contract and a provider class for this content provider, as well as entity classes for messages and peers, using the same package structure as in the previous assignment.

 

You should follow these guidelines for your solution:

1.     Define two contract classes, MessageContract and PeerContract, for the content provider, ChatProvider.  Place the former two classes in the contracts subpackage of your app, and the latter in the providers subpackage of your app.  This is a practice that you will be expected to follow for all assignments for the remainder of the course.  The contracts class should define content URIs and content paths, content types, the column names for the cursor and content values, and operations for retrieving columns from a cursor and inserting them into a content values table.  The code you are provided with defines a base class BaseContract that defines some operations common to all contract classes.

2.     Define an entity class, Message, for messages entities stored in the database, and an entity class, Peer, for chat peer entities stored in the database.  You should have done most of this for the previous assignment.  This should define entity fields, an implementation of the Parcelable interface, a constructor for initializing an entity from a cursor, and an operation writeToProvider for initializing a ContentValues object (for insertion into a provider) with the fields of the entity.

3.     Use cursor loaders and the loader manager to query the provider. ChatServer activity uses the loader manager to query the content provider for a list of all messages.  ViewPeersActivity uses the loader manager to query the content provider for a list of all chat peers.  When it launches ViewPeerActivity to view the details for a chat peer, it should pass a peer entity object (as a Parcelable extra) to the subactivity; the latter will still need to use a loader manager to query the content provider for a list of all messages, filtered for a particular sender. Define all callbacks for the loader manager as methods in your activities, not in separate callback objects.  

4.     ChatServer is responsible for inserting a record for a message, and upserting a record for the sender.  For this project, it is okay if those operations are performed on the main thread, using the content resolver. 

 

Note that your apps should never use the startManagingCursor or managedQuery operations, or the constructor for SimpleCursorAdapter that takes a cursor as its argument.  However it is all right in general to use the SimpleCursorAdapter class, using the second constructor that provides a flag that indicates that the query should not be managed by the activity.  Just do not use the first, deprecated constructor that causes queries to be managed on the UI thread.  

 

Your solution should consist of two apps, Chat-Client-Oneway and Chat-ServerOneway.  The client app is unchanged from previous assignments.  The chat server should follow the guidelines described above above: Use cursor loaders and the loader manager for querying all messages received so far, and for querying all peers from whom we have received messages.  It is okay to “upsert” peer and message information into the database, when a message is retrieved, on the main thread.  We will fix this in the next assignment, when we define asynchronous content resolvers.