Android Best Practices - Thoughts from the Trenches

Android Best Practices
Anuradha Weeraman

What makes a good Android app
● Responsiveness
● Resource-conscious
● User experience and UI
● Co-exist and interact with other apps
● Follows good engineering standards

Responsiveness
● Do not block the UI thread with heavy work
● Offload them to a worker thread
● Respond to user input within 5 seconds
● Broadcast receiver must complete in 10 seconds
● User perceives “slowness” if it takes more than 200ms
● Always update the user on progress
● Avoid modal views and dialogs
● Render the main view and fill in data as it arrives

Responsiveness
private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> {
// Do the long-running work in here
protected Long doInBackground(URL... urls) {
int count = urls.length;
long totalSize = 0;
for (int i = 0; i < count; i++) {
totalSize += Downloader.downloadFile(urls[i]);
publishProgress((int) ((i / (float) count) * 100));
// Escape early if cancel() is called
if (isCancelled()) break;
}
return totalSize;
}
// This is called each time you call publishProgress()
protected void onProgressUpdate(Integer... progress) {
setProgressPercent(progress[0]);
}
// This is called when doInBackground() is finished
protected void onPostExecute(Long result) {
showNotification("Downloaded " + result + " bytes");
}
}
new DownloadFilesTask().execute(url1, url2, url3);

Enable StrictMode
public void onCreate() {
if (DEVELOPER_MODE) {
StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder()
.detectDiskReads()
.detectDiskWrites()
.detectNetwork() // or .detectAll() for all detectable problems
.penaltyLog()
.build());
StrictMode.setVmPolicy(new StrictMode.VmPolicy.Builder()
.detectLeakedSqlLiteObjects()
.detectLeakedClosableObjects()
.penaltyLog()
.penaltyDeath()
.build());
}
super.onCreate();
}

Performance Pointers
Avoid creating short-term temporary objects if you can.
Fewer objects created mean less-frequent garbage
collection, which has a direct impact on user experience.
Avoid creating unnecessary objects

If you don't need to access an object's fields, make your
method static. Invocations will be about 15%-20% faster.
It's also good practice, because you can tell from the
method signature that calling the method can't alter the
object's state.
Prefer static over virtual

When declaring constants in a class, always use ‘static
final’ as it reduces the amount of work that the VM has to
do at runtime.
Use ‘static final’ for constants
static final int intVal = 42;
static final String strVal = "Hello,
world!";

It's reasonable to follow common object-oriented
programming practices and have getters and setters in
the public interface, but within a class you should always
access fields directly. Virtual method calls are expensive,
much more so than instance field lookups. Direct field
access is about 7x faster than invoking a trivial getter.
Avoid internal getters/setters
i = getCount()Replace
i = mCountWith

Question time
public void zero() {
int sum = 0;
for (int i = 0; i < mArray.length; ++i) {
sum += mArray[i].mSplat;
}
}
public void one() {
int sum = 0;
Foo[] localArray = mArray;
int len = localArray.length;
for (int i = 0; i < len; ++i) {
sum += localArray[i].mSplat;
}
}
public void two() {
int sum = 0;
for (Foo a : mArray) {
sum += a.mSplat;
}
Place these three functions in ascending order of speed.

ARM CPUs that Android devices use do not have an FPU
and is therefore around 2x slower when performing
floating point calculations than integers as the calculation
is performed in software. Avoid using floating point
wherever possible, and keep note of this when optimizing
performance in hotspots.
Avoid using floating point

Android libraries have been extensively optimized for the
constrained runtime environment. Use the provided
libraries for best performance. For example, System.
arraycopy() is about 9x faster than a hand-coded loop in a
JIT environment.
Use the libraries

Apps that use native code from the Android NDK are not
necessarily the most performant. There’s overhead
associated with the Java-native transition and the JIT can’
t optimize across these boundaries.
As a rule of thumb, use the NDK when you have existing
codebases that you want to make available on the
Android, and not for speeding up parts of your application.
Use native methods carefully

Measure the performance of the app using ‘traceview’ and
DDMS (now Android Device Monitor).
Always measure

Resource-conscious
● Mobile devices are resource constrained environments
● Your app must play nice in this environment
● Respect user’s preferences
● The devices may not have all the hardware you need
● Release resources when you don’t need them

Question time
What is a wake lock?

Resource Pointers
A capability that can be used to drain your battery
efficiently and quickly. Always ask the question, “Do I
need to use a wake lock?”
● Use the minimum level possible, when required.
- PARTIAL_WAKE_LOCK
- SCREEN_DIM_WAKE_LOCK
- SCREEN_BRIGHT_WAKE_LOCK
- FULL_WAKE_LOCK
● Release as soon as you can
● Specify a timeout
Don’t overuse wake locks

Resource Pointers
Flag CPU Screen Keyboard
PARTIAL_WAKE_LOCK On* Off Off
SCREEN_DIM_WAKE_LOCK On Dim Off
SCREEN_BRIGHT_WAKE_LOCK On Bright Off
FULL_WAKE_LOCK On Bright Bright
PowerManager pm = (PowerManager) getSystemService(Context.POWER_SERVICE);
PowerManager.WakeLock wl = pm.newWakeLock(PowerManager.SCREEN_DIM_WAKE_LOCK, "My Tag");
wl.acquire();
..screen will stay on during this section..
wl.release();

Resource Pointers
The FULL_WAKE_LOCK has been deprecated in favor
the FLAG_KEEP_SCREEN_ON attribute which is better
at handling this when the user moves between apps and
requires no special permission.
getWindow().addFlags(
WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON)

Resource Pointers
Only transfer data in the background if it’s enabled by the
user.
Respect user preferences
boolean backgroundDataEnabled =
connectivityManager.getBackgroundDataSetting()
Note: This is deprecated on ICS and above and will
instead show getActiveNetworkInfo() as disconnected.

Resource Pointers
● By default, the service would keep restarting when
killed by the runtime
● By setting START_NOT_STICKY it would not
Allow the runtime to kill your service
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
//TODO do something useful
return Service.START_NOT_STICKY;
}
}

Resource Pointers
As with activities the Android system may terminate the
process of a service at any time to save resources. For
this reason you cannot simple use a TimerTask in the
service to ensure that it is executed on a regular basis.
Use receivers and alarms to trigger your service
Calendar cal = Calendar.getInstance();
Intent intent = new Intent(this, MyService.class);
PendingIntent pintent = PendingIntent.getService(this, 0, intent, 0);
AlarmManager alarm = (AlarmManager)getSystemService(Context.ALARM_SERVICE);
// Start every 30 seconds
alarm.setRepeating(AlarmManager.RTC_WAKEUP, cal.getTimeInMillis(), 30*1000, pintent);

Resource Pointers
When scheduling updates, use inexact repeating alarms
that allow the system to "phase shift" the exact moment
each alarm triggers. If several alarms are scheduled to
trigger at similar times, this phase-shifting will cause them
to be triggered simultaneously, allowing each update to
piggyback on top of a single active radio state change.
Use inexact alarms
int alarmType = AlarmManager.ELAPSED_REALTIME;
long interval = AlarmManager.INTERVAL_HOUR;
long start = System.currentTimeMillis() + interval;
alarmManager.setInexactRepeating(alarmType, start, interval, pi);

Resource Pointers
● Services should only be running when needed
● Perform the activity in an AsyncTask
● Kill the service when the task is complete
Kill your own service when work is done
stopSelf()

Resource Pointers
● Explicitly specify uses-feature node in the manifest for
every hardware/software feature used in the app
● Mark essential features as required
● Mark optional features as not required
Declared required hardware and check for availability
when using them
<uses-feature android:name="android.hardware.bluetooth" />
<uses-feature android:name="android.hardware.camera" />

Resource Pointers
Check for API availability before using features
PackageManager pm = getPackageManager();
boolean hasCompass = pm.hasSystemFeature(PackageManager.
FEATURE_SENSOR_COMPASS);
if (hasCompass) {
// do things that require the compass
}

Question time
How does Google Play make use of the uses-feature
declarations?

Question time
Are permissions required anymore when the uses-feature
element is present in the manifest?

User experience & UI
● User experience should be your first priority
● Don’t copy UI paradigms from other platforms
● Respect user expectations on navigation
● The back button should always navigate back through
previously seen screens
● Navigating between application elements should be
easy and intuitive
● Use notifications judiciously - time sensitive / involves
another person
● Use dialogs for feedback, not notification

UX/UI Pointers
Respect user expectations of navigation

UX/UI Pointers
Don’t override the menu button to make it do something
other than displaying the contextual menu. It’s important
to keep the metaphors consistent to provide a good user
experience.
Don’t override the menu button

UX/UI Pointers
While it’s easy to build for just one orientation such as
portrait, there are some devices where the orientation
changes when the physical keyboard is activated. A good
user experience needs to cater to different orientations
intelligently.
Support both landscape and portrait modes

UX/UI Pointers
● Start with vector or high res
raster art
● Scale down and optimize for
supported screens and
resolutions
● Use device independent pixels
● Use fragments to re-use design
elements across different form
factors
● Optimize the layout for the
available screen real-estate
Don’t make assumptions about screen size or
resolutions

Co-exist and interact with other apps
● Your app is just one of many on
the device
● The more it gets integrated into
the ecosystem of the device, the
easier it is for the user and better
the experience

Integration Pointers
● Use intents to leverage other people’s apps
● Can pass data back and forth between applications
● Use intent filters to share functionality with other apps
● Use content providers to expose access to an app’s
content for consumption by other apps and widgets
Leverage existing apps

Follow good engineering practices
● Don’t use undocumented APIs!!
● Android comes with a number of engineering tools for
ensuring technical quality of your app
● Use these tools during development and testing to make
sure that your app follows good engineering practices
and for troubleshooting performance issues that may
degrade the user experience

Question time
Name a tool that come with the Android SDK that can be
used for performance analysis and profiling during
development?

Static / structural analysis
● Android comes with a tool called lint that can be used for
identifying and correcting structural problems with your
code
● Each detection has an associated description and
severity level so it can be prioritized
● Can be invoked directly from the command-line,
automated build system or directly from Eclipse

● Android comes with a tool
called hierarchyviewer which
is now part of the Android
Device Monitor that can be
used for analyzing layout
rendering performance
● Can be used in combination
with lint to discover and fix
performance issues that
affect responsiveness
● The Pixel Perfect window in
hierarchyviewer can be used
for getting the layout just right
Layout optimization

● ‘traceview’ is a tool that can be used for viewing
execution logs produced by an app for method profiling
purposes.
● Traces can be created from within the code or from the
DDMS tool, depending on how granular you want the
traces
Profiling
// start tracing to "/sdcard/calc.trace"
Debug.startMethodTracing("calc");
// ...
// stop tracing
Debug.stopMethodTracing();
● ‘dmtracedump’ is an alternate tool that can be used for
visualizing the call stack from trace log files

Profiling
● systrace helps you analyze how the execution of your
application fits into the larger Android environment, letting
you see system and applications process execution on a
common timeline. The tool allows you to generate highly
detailed, interactive reports from devices running Android
4.1 and higher.

● RoboGuice is a framework that brings the simplicity and
ease of Dependency Injection to Android, using Google's
own Guice library.
Dependency Injection
class AndroidWay extends Activity {
TextView name;
ImageView thumbnail;
LocationManager loc;
Drawable icon;
String myName;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
name = (TextView) findViewById(R.id.name);
thumbnail = (ImageView) findViewById(R.id.thumbnail);
loc = (LocationManager) getSystemService(Activity.
LOCATION_SERVICE);
icon = getResources().getDrawable(R.drawable.icon);
myName = getString(R.string.app_name);
name.setText( "Hello, " + myName );
}
}
class RoboWay extends RoboActivity {
@InjectView(R.id.name) TextView name;
@InjectView(R.id.thumbnail) ImageView thumbnail;
@InjectResource(R.drawable.icon) Drawable icon;
@InjectResource(R.string.app_name) String myName;
@Inject LocationManager loc;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
name.setText( "Hello, " + myName );
}
}

YAMBA - Yet Another Micro-
Blogging Application
Requirements
1. Build a Twitter-like micro blogging application.
2. User can view a stream of statuses fetched from a server.
3. User can update preferences to specify user’s details.
4. The statuses are fetched from the server in the background and
persisted locally.
5. The background process that fetches the statuses is started
when the device boots.
6. The background process is started and stopped depending on
the available network connectivity.
7. A timeline view shows the latest stream of statuses from local
storage.

Question time
What are the structural building blocks in Android
that can be used to build apps?

YAMBA - Yet Another Micro-
Blogging Application

Android Best Practices - Thoughts from the Trenches

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