Android: Ring Control

I've been playing around with a little Android application for a few weeks now, while taking occasional breaks from working on other, more "real" Android projects.

It's called Ring Control, and it puts your phone on vibrate (or silent, depending on your preferences) mode if you put it upside-down in your pocket, or lay it face-down on a table (again, depending on your preferences).

The idea is pretty simple, and the implementation was too, at least initially. It's easy: Get a reference to the SensorManager, tell it you want to know about orientation changes, calculate the degrees of pitch in the orientation, and set the ringer mode depending on the pitch value. I gave it about 50 degrees of latitude (or is that longitude) in either direction to keep it from being too touchy about device orientation.

The app consists mainly of two parts: The UI screen (for starting and stopping Ring Control and setting preferences), and the background service that actually controls the ringer. Probably the smallest Android app I've written since that "Hello World" app back in '08.

As I said, the idea is simple, but it turns out to be kind of a tricky problem. The "hard" part (well, not hard, now that I know what to do) is making it work like you would expect it to work.

As it happens, Android is pretty conservative about things like memory and battery power, and isn't keen on letting background services just sit there and nibble on the CPU while doing nothing else. ("nothing else" in this case defined as "not having any clients asking them for things"). So after about 1/2 hour, my background service would just stop, with no notifications or anything else. Since the whole point of Ring Control is to turn your ringer to vibrate and keep the phone quiet, it doesn't seem too useful to have it just stop suddenly, letting your phone spew out a loud "riiiiinnng..." (or other obnoxious ringtone) while you're in a funeral or something and need for it to be quiet.

I started reading about the various ways to tackle the problem, and read about "wake locks" and other things that you can use to poke at the phone's CPU to keep it alive so your service will work. That seemed like a good way to eat up batteries, and there was still nothing in the idea that would seem to actually ensure that the service kept working.

So, no.

As it turns out, there is an accepted way to keep a background service running, and that is to use the AlarmManager system service. Essentially, you schedule a repeating alarm, say, every 5-10 minutes, and the "alarm" is an "Intent" (Android-speak for "thing that runs something") telling the AlarmManager to start your service (or activity or broadcast message). It seems like kind of a goofy way to do it, really. I read about it, and thought "Seriously? I have the AlarmManager start me at regular intervals?" Whatever works, I guess. In any case, I set it up so the "start" signal just keeps the service running if it's already running, instead of starting another copy.

Having done that, the service now runs as long as it's supposed to, and doesn't poop out spontaneously.

Ring Control turned out to be pretty popular on the Android Market, with a lot of people downloading it and e-mailing me about it and commenting on it in the Android Market. (Best comment so far: "I give it 3 stars. I wish it would show movie times." Huh?) One feature people asked for was the ability to run it automatically when the phone boots.

Like a lot of things with Android, I seem to look in the wrong place initially for information about how to do something. I started thinking about some kind of "startup folder" metaphor somewhere, found nothing.

The way to get a service or application to run at startup is to create a "BroadcastReceiver", a class that receives a broadcast notification from the OS when something happens, and assign to it a key. There are keys for all kinds of events (e.g. incoming call, SMS message, blah blah blah). The one I was interested in was "android.intent.action.BOOT_COMPLETED." This notification gets sent to applications that want to know about it, even if they're not running. Android pulls a BroadcastReceiver out of bed and calls its onReceive() method, passing it some info about what's starting it. In my case, I just start the Ring Control service in my BroadcastReceiver, and that's it.

Now that that's done, I've got some other ideas on how to use the orientation sensor for something interesting.

Overall, I kind of enjoy walking around with a device with all this stuff on it. It has a compass, orientation sensors, GPS, internet access, audio and video playback (makes a good iPod), functions as a mirror when the screen's turned off, makes a good hand warmer if you surf the web a lot, is heavy and chunky enough to ward off an attacker, and has changed my life in general: I no longer have time to sit in meetings getting annoyed at people playing with their fancy phones. I'm too busy playing with my phone.