This was probably the most technical chapter so far. Threads, game loops, timing, using interfaces along with the Activity lifecycle, and so on… it's an awfully long list of topics to cram in.
If the exact interrelationships between these things are not entirely clear, it is not a problem. All you need to know is that when the user starts and stops drawing with their finger, the LiveDrawingActivity class will handle starting and stopping the thread by calling the LiveDrawingView class's pause and resume methods. It achieves this via the overridden onPause and onResume methods, which are called by the OS.
Once the thread is running, the code inside the run method executes alongside the UI thread that is listening for user input. As we call the update and draw methods from the run method at the same time as keeping track of how long each frame is taking, our app is ready to rock and roll.
We just need to allow the user to add some particles to their artwork, which we can then update...