1. Reactive Android Development
CS T & CS T
Summer 2016
Services, Threads, and "Push (Pull)"

2. Running jobs in the background
Last time, we talked about the Intent Service
Can not interact directly with the UI
Results must be sent to the activity for it to handle
Work requests run sequentially
If one request blocks, all others must wait until it is finished
An operation running on an intent service can not be interrupted
If the result is no longer desired, it must be ignored after it arrives.

3. Running jobs in the background
But earlier, we talked about Services
Just a component without a UI and that can be running in the background
IntentService is a subclass
Regular Services run in the main thread of the application
If performing an intensive or blocking task, it should launch a thread

4. Service
Lifecycle

5. AsyncTask Very simple way to do work in the background
doInBackground
Code that will execute in the background
onPostExecute
Code that will execute in the main thread
Good for GUI updates.
Can be cancelled!
Tasks are Queued
Since HONEYCOMB, AsyncTasks execute sequentially to reduce bugs caused by parallel execution.

6. Threads Regular Java Threads Lifecycle is not managed by Android
Java no longer provides mechanisms for killing threads directly
My approach:
Ensure that the main loop can't block indefinitely
Check a 'should continue' member variable at each loop iteration
Basically the same as the isCancelled method for AsyncTask

7. "Push" Notifications Most WiFi IP addresses are not routable
This isn't true on campus, but is likely to be true at a coffee shop
How can a central server contact devices?

8. "Push" Notifications
How can a central server contact devices?

9. "Push" Notifications How can a central server contact devices?
Let's assume that it can't!

10. "Push" Notifications How can a central server contact devices?
Let's assume that it can't!
What if the device contacted the server and waited for a response?

11. "Push" Notifications
Basically, I'm implementing push notifications as a sort of slow HTTP server.
The client connects and tries to read the server with a long timeout.
The server only replies when it has something to send.

12. The Layout