Android Development Gotchas

Android Development Gotchas

This isn’t designed to be a definitive list of unexpected occurrences while developing for Android, but it is a list that I scratched down while I was picking up some skill for myself. It won’t save you from every issue but there may be cases where you can stop and think “Yeah, Dave told me that would happen”.

My development environment included Eclipse 3.5 with the Google ADT plugin and all testing was against a rooted HTC Desire and unroot Samsung Galaxy SII both running Android 2.2, development code targeted Android 2.1. Problems may be an issue with ADT, HTC, Samsung, Android 2.1 or 2.2, rooting or the specific hand sets 🙂

Java 1.6 on a Dell XPS 1530 running Ubuntu 10.10, if that matters.

Virtual Devices

I found these too slow and unusable.

Early on in development I gave up trying to use the the ADT virtual devices and tested directly against the target hardware devices. Luckily for me the application was for internal use only and would be released to specific clients with specific handsets, but I was disappointed at how slow the VMs were start and how slow they ran. The develop-deploy-test cycle was just too slow using the ADT.

Virtual Devices Cannot Support Bluetooth

ADT Virtual Devices cannot support Bluetooth, and as our application includes Bluetooth communication this was another reason ADT development was excluded.

Inconsistent Bluetooth Support Between Vendors

This was a strange one to us, and not one that we have (to this point) been able to resolve although my guess is that it is a problem with the HTC code.

Our application involved having a file sent to the phone using OBEX over Bluetooth. No problems so far. Pair the devices, enter the code, initiate the file transfer.

The Samsung Galaxy SII displayed the preferred behaviour, where the incoming file prompt the phone user to accept the file, but also provides a checkbox to always accept files from this device. If you don’t select the checkbox then you are prompted each time a file arrives, but you are still able to check the box later on.

When the first file arrives, HTC Desire asks if you want to allow the remote device to synchronize contacts, and whether you always want to allow this. If you don’t allow this, you aren’t able to get to the next step where you accept the file. If you don’t accept contact swap all the time you’ll be prompted each time. Regardless of whether you swap contacts or not, you must accept each file as it comes in. Accepting every file manually is not our preferred behaviour.

Android Apps Run on a Single Thread

Some of this cuts into Android’s Handlers, task scheduling and communication across threads, but it may come as a surprise during development that all standard processing occurs on a single Thread. This is something that you’ll want to play with and become familiar with as it may be surprising that UI performance is impacted by Runnables and Services.

I do recommend you have a play.

Creating new Threads is one option, although Android’s AsyncTask is the preferred mechanism for truly asynchronous processing that doesn’t freeze the GUI.

… and that Thread is a UI Thread

Following on from the previous point, the main thread is a UI thread and that that thread is only active when the UI is active. Sort of. Check the Android fundamentals processes and threads page, but just be aware that if you want something to process while (for example) the screen is locked, you need to be aware of the processing thread.

Beware Empty Elements in XML Layouts

If you’re like me, you like tidy XML and prefer an empty element (where applicable) to an element which is not ’empty’ but has no child elements.

	<!-- this element has no children -->
	<ListView android:layout_width="fill_parent" android:layout_height="wrap_content" android:id="@android:id/list"></ListView>
	<!-- this is an empty element -->
	<TextView android:id="@android:id/empty" style="@style/EmptyContent" android:text="@string/emptyResponseEntries" />

In this example, the TextView is empty and causes no problems, but the ListView will. If you make the ListView an empty XML element, you can write items to the List, but they won’t show up on the screen. There won’t be any error reported, it just won’t show up.

Can’t Read Property Defaults

Property defaults were also something I found perplexing. If you specify a properties.xml file, each property is able to define a default value. Likewise when reading properties via the SharedPreferences you can specify a default value if the property doesn’t exist, but the two default values aren’t related. You can’t read the default value as defined in the preferences.xml file for use elsewhere, the API doesn’t provide access.

Note that recommended properties management is via the PreferenceFragment

Notifications Can Be Empty

I found this one amusing. It is possible to create an empty Notification using new Notification(), specify a notification sound, and annoy users without providing any indication of where the annoying sounds are coming from.

Great Developers Are Not Afraid to Experiment

As a moderator on the JavaRanch, I often come across people asking “What would happen if I executed the following code”. Many times the author of such posts can answer the question by copying and pasting his/her code into a Java main() method and running it. Some might chalk these posts up to being lazy, but, clearly, taking the time to write a post on a message board – often signing up as a member for the first time – takes some amount of effort as well. With that, I’m going to be go with the assumption developers avoid experimenting with code because they are scared or unsure of their own knowledge. Besides which, if it is a matter of laziness, there’s not much advice I can give except to say “Don’t be lazy”.


Why is experimenting with code can be scary

In my experience as a teacher, development lead, and moderator I often come across developers who are unsure of their own knowledge. Often times they don’t fully understand what it is the code is doing and are afraid to experiment for fear it will either demonstrate their own personal weakness or harm the existing code. To them, I believe that experimenting is most crucial, if only because some of the doubts and questions that linger in their head can often be answered in an surprisingly short amount of time. If you are staring at a piece of code, puzzled by what you do not understand, take my advice: Step back and play 20 questions, ask yourself “What are questions I have about this code that can be answered with a simple yes/no?” then set up test code to answer each question. Once you have your answer, your doubt about the application should vanish, replaced by first-hand knowledge of what is going on. Keep in mind that sometimes these experiments lead to even more questions, but that’s good; it’s part of the learning process. In those cases, perform even more experiments on the code.

What is an experiment?

What constitutes an experiment? Oftentimes, it involves just writing a short line or two of code, then writing a logging statement, or, more commonly, if you don’t have a logger, a System.out.println() statement that displays the value of some variable or object. For example, if you don’t know why a method is behaving a certain way, add a dozen output statements throughout the code so you can follow two things: 1) the path the code is taking and 2) the value of the data throughout the code. Many times, you may be staring at a section of code, wondering why it’s not working, only to find out that section of code is never reached at run-time. Experimenting can be about changing values and recording the inputs, but sometimes its just about outputting where/what you think a process is doing.

Some people will recommend a debugger for experimentation but I’m not one of them. Aside from often being unwieldy and confusing to use, especially for beginners, sometimes running code through a debugger can affect what it outputs. For example, in a server environment, remote debuggers can be especially difficult to use. Services may have transaction timeouts of 30 seconds, and pausing the code in the debugger can cause an exception to be thrown before the method is complete. If you like using debuggers, more power to you, but as someone who has used both output statements via logging tools and debuggers, I greatly prefer the logging tools. Primarily, this is because the output statements give you more of a trial and error structure to work with: either a test succeeded, or it failed, and the output is all there in front of you.

Stand-alone Safe Experiments

The easiest and safest experiments are those you create that are completely separate from any other code. In terms of Java and Eclipse, this is akin to creating a new Workspace and a new Java Project to run the test code in. Every developer should have a temporary, throw-away workspace like this to perform low-level Java tests with. Simply create a file which in some way asks the question you want answered, and execute the program to evaluate the results.

Safe Experiments within Existing Code

Let’s say the code is highly framework dependent, such as often is the cases with J2EE and database-driven applications. For example, creating a temporary workspace to house your test case may be too cumbersome to implement. In such a case, you can run the experiment inside your existing code provided you are careful and follow some general guidelines:

  • If you are working with code that is backed by a repository, such as Subversion, CVS, ClearCase, etc, make sure your experimentation code does not get checked in or you may end up with applications such as this, this, or even the impossible (the last one). The DailyWTF has literally thousands of such cases. It is perfectly fine to experiment, just be careful to cleanup when you are done!
  • If you are working with code that is *not* backed by a repository, then install a developer repository! I cannot tell you enough the power and value of using a coding repository for all development work. In lieu of that, though, you should just make a copy of the project and/or workspace and experiment with the copy, keeping the original intact.
  • If you are working with code that connects to a database, make sure it’s not one other developers use. Making changes to a shared database as part of a test could affect other developers, so, if possible, you should have your own local copy of the database. This does not mean you should have a production database, but merely a copy of a QA or Development database

Final Thoughts
In my experience, one of the things that separates a great developer from the rest of the pack is that the great developer fully understands the code they are writing. When a bug appears (even great developers can cause bugs), this person often has a good idea where to look for the problem right away, and save valuable support time. Ultimately, if you ever find yourself mystified by your own code base, run some experiments and learn why things work the way they work. You’ll be a better developer for it!