Android Best Practices - Thoughts from the Trenches

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Android Best Practices - Thoughts from the Trenches

  1. 1. Android Best Practices Anuradha Weeraman
  2. 2. What makes a good Android app ● Responsiveness ● Resource-conscious ● User experience and UI ● Co-exist and interact with other apps ● Follows good engineering standards
  3. 3. A classic
  4. 4. 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
  5. 5. 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);
  6. 6. 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(); }
  7. 7. 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
  8. 8. Performance Pointers 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
  9. 9. Performance Pointers 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!";
  10. 10. Performance Pointers 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
  11. 11. 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.
  12. 12. Performance Pointers 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
  13. 13. Performance Pointers 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
  14. 14. Performance Pointers 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
  15. 15. Performance Pointers Measure the performance of the app using ‘traceview’ and DDMS (now Android Device Monitor). Always measure
  16. 16. 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
  17. 17. Question time What is a wake lock?
  18. 18. 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
  19. 19. Resource Pointers Don’t overuse wake locks 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();
  20. 20. 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. Don’t overuse wake locks getWindow().addFlags( WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON)
  21. 21. 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.
  22. 22. 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; } }
  23. 23. 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);
  24. 24. 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);
  25. 25. 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()
  26. 26. 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" />
  27. 27. 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 }
  28. 28. Question time How does Google Play make use of the uses-feature declarations?
  29. 29. Question time Are permissions required anymore when the uses-feature element is present in the manifest?
  30. 30. 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
  31. 31. UX/UI Pointers Respect user expectations of navigation
  32. 32. 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
  33. 33. 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
  34. 34. 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
  35. 35. 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
  36. 36. 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
  37. 37. 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
  38. 38. Question time Name a tool that come with the Android SDK that can be used for performance analysis and profiling during development?
  39. 39. 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
  40. 40. ● 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
  41. 41. ● ‘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
  42. 42. 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.
  43. 43. ● 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 ); } }
  44. 44. Some bedtime reading
  45. 45. 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.
  46. 46. Question time What are the structural building blocks in Android that can be used to build apps?
  47. 47. YAMBA - Yet Another Micro- Blogging Application

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