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In this video tutorial, we extend the Utopian Rocks flutter application by adding an information drawer. This drawer displays information about the application to the users and it allows the users to update the application. The drawer uses the package information library and the GitHub releases API; both of which get served through a second BLoC structure.
The Business Logic Component pattern is very flexible. In the last tutorial, we used it to serve the main contributions to the user interface. In the interest of separating the concerns of our application, it makes sense to create a second BLoC structure to handle the serving of the application metadata to the user. Not only does this make the code more modular but it also allows us to inject the BLoC into areas of the application where it is needed.
If our widget tree looks like the diagram above, we have two separate BLoC providers. The first BloC Provider is in the root widget. This provider can give the state of the BLoC to any of the widgets below it on the tree. Our second BloC Provider appears further down the tree and it can only give its associated BLoC to widgets that are directly below it on the tree. In this pattern, we are able to selectively update and change the widgets that need dynamic information while minimizing the rebuilding of widgets that do not.
In the new BLoC, we use both deferred and future based observables. These types of Streams are perfect for the data that is inside of our BLoC because the data is a single event. With a normal stream, you may only listen to the stream a single time. With a broadcast stream, you can listen to the stream as many times as you need but once the stream is closed, it can't be reopened. With the Deferred and Future Observables, we have streams that are both re-usable and re-buildable.
When the drawer is opened, the application subscribes to the _infoStream stream from the information BLoC. When the drawer is closed, this stream is discarded by the flutter framework because the entire drawer widget tree is dissembled. With a normal stream, if the user was to re-open the drawer, the data would never re-appear in the box. The same is true for the button on the drawer. When the button is pressed, it fires off to the GitHub API to check to see if there is a new release. Also, the button uses the _infoStream stream and the _releases Stream to determine if there is a new release or not. If either doesn't reopen, then the entire process would fail.
The Source Code for this video may be found here: https://github.com/tensor-programming/utopian-rocks-demo/tree/tensor-programming-part-2
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