Thursday, October 23, 2008


My second Android application is a special-purpose calculator for solving some of the problems which often arise when it comes to paying the bill in a restaurant - like computing the tip or splitting the bill among N people. This seemed like a reasonably useful application for a device which the user always carries around and one that is very simple to do. In fact it turns out that tip calculators are somewhat the "hello world" equivalent of mobile application development. To be useful, the user experience would have to be very simple and rapid - not necessarily obvious with the clunky keyboard setup of the G1!

The calculator uses a table view of buttons as a virtual keypad for inputting numbers and another table on the top to display the results. The display table is fully specified in the XML layout file, while the cells of the keypad table are generated by the code. There is a menu to select the input fields (price, tax, tip, number of people and currency exchange rate) which can also be selected by touching the specific fields on the display using customized touch-event handlers.

When the keyboard is active, the virtual keypad is hidden and the activity intercepts keystroke events for updating the display. The application is not using any input widget, but raw events to update the display grid at every key-stroke.

The code is open-source and can be found at


While on paternity leave, I wrote this first Android application as a kind of remote baby monitor - even though I would never dare to suggesting using it as such in public... The basic functionality is that when running the application monitors the sound volume through the microphone and if it exceeds a certain threshold automatically dials a number which previously has been configured.

Based on existing examples which come with the SDK distribution it is pretty easy to put together the basic application skeleton - including the XML description of the UI layout. If you don't know what you are looking for the documentation on the Android SDK site is a bit sparse but is great to look up details.

The application consists of an Activity, the Android abstraction for a single self-contained screen with some associated behavior and user interaction. This screen has a layout and a main menu defined in XML and provides framework methods to handle I/O and life-cycle events. For simple apps we can also use periodic event handlers to trigger actions directly from the UI thread.

It seems the only way to currently measure the sound input at the microphone is to run the MediaRecorder and use its getMaxAmplitude method to periodically get the maximum sound level since the last call. Setting up the recorder to write to "/dev/null" - the Unix special bit blackhole works just fine, which avoids filling up the flash card and having to deal with cleanup. For added benefit, there is a special graphical widget which displays a bar power meter with the current sound level from 1-10 in green and red depending on the threshold.

When it comes to calling the phone number, Android supports a intents - a framework of publish-subscribe signals which an application can send to get something done without knowing who is registered to handle them. In this case, the standard system phone application happens to be registered for the ACTION_CALL intent which is used to call a number.

The configuration is nearly automatic. A hierarchy of preferences can be described in XML and then loaded to generated a standard preferences screen which happens many common cases: on/off checkbox options, 1 out of N selection lists, text entry fields, etc. When the preference screen returns it has automatically store the results in the applications default preferences DB instance.

Thus writing a simple Android application with a main menu, some settings and a bit of behavior is really that simple.

The application code is open-source and can be found at Application package can be downloaded from the same site or is available through the Android Market.

Wednesday, October 22, 2008

Android / T-Mobile G1

I have been using the new T-Mobile G1 as my primary phone for a while now. It is the first phone which runs the open-source Android mobile software stack. I agree with most of the reviewers that the G1 or even the Android software is no iPhone when it comes to stylish elegance, attention to detail and consistency in the user experience. However, this is somewhat besides the point. Android is a developers dream - designed from the ground up as a 3rd party application delivery platform. I have also played around with the application development toolkit and written 2 small Android applications - which even for somebody without any prior experience in Java or mobile device programming is surprisingly easy.

The main criticism for the G1 hardware is that it seems to have been designed by former soviet industrial planers - I can't quite figure out if it is meant to be retro Brezhnev or Khrushchev era styling... I would also prefer a 100% touch-screen driven device instead of the neither fish nor fowl physical design compromise which a sliding phone requires. On the other hand, lot's of people seem to think the keyboard is a great advantage over the iPhone and since the G1 has all the imaginable hardware features (3G, WiFi, bluetooth, camera, touch-screen, keyboard, GPS, accelerometer, compass, etc.) I makes for a great eval and development platform for the Android software before it is ported and released on hardware which maybe will make some more radical design choices - e.g. an iPhone class 100% touch-screen only phone (HTC Touch HD anybody...) or a BlackBerry/Nokia style high quality fixed keyboard body without touch-screen. The G1 feels solid and can't really be faulted for anything other than being somewhat unrefined and uninspired - at least next to an iPhone.

The software stack is surprisingly stable and mature for a product which is barely out of the door. The tight integration with Google gmail, calendar, contacts and IM is nice for people who mostly use it. In the beginning the sync for contacts and calendar acted up a few times and got stuck, but since the server side is the master copy anyway, it is easy to get unstuck again by simply erasing the data for the application in question.

In general the current release of Android lacks monitoring and management. It's all nice when things work, but when something is funny there is very little even a power user can look at - short of connecting the USB port and using the development bridge (adb shell...). Since Android gives developers far reaching powers - including running in the background or continuously as a service - the user is often at the mercy of the application developer being reasonable - specially when it comes to being power efficient - which is probably one of the most critical things on a mobile device. There is very little the user can currently do to even see what the apps are doing and override their behavior once they are installed - other than uninstalling them again, if the user can figure out which app might be causing the problem.

Many apps have been developed purely on the emulator and the hope is that once the developers themselves have real hardware in their hands and see how their app kills the battery in 3h they will maybe figure out that polling the GPS for current position every 3s is maybe not such a smart idea - even though location aware application seemed like such a cool idea in concept. Half the apps currently in the Android Market are somehow location based - and the GPS on the G1 is one of the worst battery killer...

The G1 is certainly a great starting point to make Android real and I can only imagine what potential it has for development and research in mobile systems and applications. Personally, I am still hoping for a slicker more elegant device - with only a large high-quality touch screen and no moving parts.