Building First Class Android SDKs - Øredev 2015

Fabric, formerly Crashlytics, is well-known for its focus on SDK quality, and has been deployed on billions of devices. In this session, attendees will learn the skills to develop and distribute SDKs for Android. We’ll cover an overview of Fabric, deep dive into technical decisions we made, and present the learnings on developing an SDK for stability, testability, performance, overall footprint size, and, most importantly, exceptional ease of implementation. Over the course of the session, we'll uncover and explain many of the challenges we encountered when building SDKs at Twitter. Topics include device feature detection, supporting multiple application types (from Widgets to Services to Foreground GUI applications), API design, deploying artifacts, and coding patterns to support developer customization. We'll conclude with advanced topics, from less-known but very useful tricks to minimizing impact on application start-up time to reducing memory footprint and persistent CPU use.

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Transcript

1. App to App Designing Local APIs on Android Ty Smith Android Engineer at Twitter 1 @tsmith
2. 2 @tsmith
3. 3 @tsmith
4. 4 @tsmith
5. Integration Requirements • Get Note(s) • List Notes • Create/Update Notes • Delete Notes • Account Sync • Get Preferences 5 @tsmith
6. Android Components Needed 1. Intents 2. Content Provider 3. Account Manager 4. Sync Adapter 5. Inter Process Communication 6. Permissions 6 @tsmith
7. Intents Overview • Simple message between two components • Bundle - key/value data • Limited payload size (1MB) • Inefficient for batch operations • Defined Action 7 @tsmith
8. Intents Standard Actions • ACTION_SEND • ACTION_SEND_MULTIPLE • ACTION_VIEW • ACTION_EDIT 8 @tsmith
9. Editing Intent Sender public void editImage(String mimeType, Uri imageUri) { Intent intent = new Intent(Intent.ACTION_EDIT); intent.setType(mimeType); intent.setData(imageUri); startActivityForResult(intent, RESULT_CODE); } 9 @tsmith
10. Editing Intent Receiver <activity android:name=".ui.IntentActivity" > <intent-filter> <action android:name="android.intent.action.ACTION_EDIT" /> <category android:name="android.intent.category.DEFAULT" /> <data android:mimeType="image/*" /> </intent-filter> </activity> 10 @tsmith
11. Editing Intent Receiver @Override protected void onNewIntent(Intent intent) { switch(intent.getAction()) { case Intent.ACTION_EDIT: if (intent.getType().startsWith("image/")) { editImage(intent.getData()); setResult(RESULT_OK, intent); finish(); } } } 11 @tsmith
12. Editing Intent Sender @Override protected void onActivityResult(int requestCode, int resultCode, Intent data) { if (requestCode = RESULT_CODE && RESULT_OK == resultCode) { Uri imageUri = data.getData(); //Update UI with new image } } 12 @tsmith
13. Intents Edit Caveats • Use copy of file • Don’t rely on setResult() • Use a ContentObserver • Check for file modified 13 @tsmith
14. Intents Custom Actions com.example.action.note.* list - view - new - create edit - update - delete 14 @tsmith
15. Intents Custom Actions public void newNoteWithContent(Uri image) { Intent intent = new Intent(); intent.setAction(NEW_NOTE); intent.putExtra(Intent.EXTRA_TITLE, "LET ME EXPLAIN YOU INTENTS"); intent.putExtra(Intent.EXTRA_TEXT, "¯\_(
    )_/¯"); intent.setData(image); startActivityForResult(intent); } 15 @tsmith
16. Content Provider A well defined database access layer • SQLite • Interact with large volumes of data • Authority 16 @tsmith
17. Content Provider URI content:// com.example / users / 1 Scheme Authority Data Id 17 @tsmith
18. Content Provider Query public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) { SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder(); switch (URIMatcher.match(uri)) { USERS_LIST: queryBuilder.setTables(MyDBHandler.TABLE_USERS); } Cursor cursor = queryBuilder.query(myDB.getReadableDatabase(), projection, selection, selectionArgs, null, null, sortOrder); cursor.setNotificationUri(getContext().getContentResolver(), uri); return cursor; } 18 @tsmith
19. Content Resolver Query Uri uri = Uri.parse("content://com.example/users"); String[] projection = new String[]{"username", “email”}; String selection = “name LIKE ?”; String[] args = new String[]{"Ty"}; String sort = “email ASC”; getContentResolver().query(uri, projection, selection, args, sort); 19 @tsmith
20. Content Provider Serving Files @Override public ParcelFileDescriptor openFile(Uri uri, String mode) throws FileNotFoundException { File path = new File(getContext().getCacheDir(), uri.getEncodedPath()); int imode = 0; if (mode.contains("w")) { imode |= ParcelFileDescriptor.MODE_WRITE_ONLY; if (!path.exists()) { try { path.createNewFile(); //TODO: Handle IOException } } if (mode.contains("r")) imode |= ParcelFileDescriptor.MODE_READ_ONLY; if (mode.contains("+")) imode |= ParcelFileDescriptor.MODE_APPEND; return ParcelFileDescriptor.open(path, imode); } 20 @tsmith
21. Content Resolver Getting Files ContentResolver resolver = getContentResolver(); URI imageUri = Uri.parse("content://com.example/images/1"); String mode = "rw+" ParcelFileDescriptor pfd = resolver.openFileDescriptor(imageUri, mode); FileDescriptor fileDescriptor = pfd.getFileDescriptor(); InputStream fileStream = new FileInputStream(fileDescriptor); //Magic here! 21 @tsmith
22. Account Manager • Accessible Account • Authentication Token • Consistency 22 @tsmith
23. Providing your own Accounts • AbstractAccountAuthenticator • AccountAuthenticatorActivity 23 @tsmith
24. 24 @tsmith
25. AbstractAccountAuthenticator addAccount @Override public Bundle addAccount(AccountAuthenticatorResponse response, String accountType, String authTokenType, String[] requiredFeatures, Bundle options) throws NetworkErrorException { final Intent intent = new Intent(mContext, AuthenticatorActivity.class); intent.putExtra(AuthenticatorActivity.ARG_ACCOUNT_TYPE, accountType); intent.putExtra(AuthenticatorActivity.ARG_AUTH_TYPE, authTokenType); intent.putExtra(AuthenticatorActivity.ARG_IS_ADDING_NEW_ACCOUNT, true); intent.putExtra(AccountManager.KEY_ACCOUNT_AUTHENTICATOR_RESPONSE, response); final Bundle bundle = new Bundle(); bundle.putParcelable(AccountManager.KEY_INTENT, intent); return bundle; } 25 @tsmith
26. AbstractAccountAuthenticator getAuthToken @Override public Bundle getAuthToken(AccountAuthenticatorResponse response, Account account, String authTokenType, Bundle options) throws NetworkErrorException { final AccountManager am = AccountManager.get(mContext); String authToken = am.peekAuthToken(account, authTokenType); if (TextUtils.isEmpty(authToken)) { final String password = am.getPassword(account); if (password != null) { authToken = serverAuthenticate.userSignIn(account.name, password, authTokenType); } } ... 26 @tsmith
27. AbstractAccountAuthenticator getAuthToken ... if (!TextUtils.isEmpty(authToken)) { final Bundle result = new Bundle(); result.putString(AccountManager.KEY_ACCOUNT_NAME, account.name); result.putString(AccountManager.KEY_ACCOUNT_TYPE, account.type); result.putString(AccountManager.KEY_AUTHTOKEN, authToken); return result; } ... 27 @tsmith
28. AbstractAccountAuthenticator getAuthToken ... final Intent intent = new Intent(mContext, AuthenticatorActivity.class); intent.putExtra(AccountManager.KEY_ACCOUNT_AUTHENTICATOR_RESPONSE, response); intent.putExtra(AuthenticatorActivity.ARG_ACCOUNT_TYPE, account.type); intent.putExtra(AuthenticatorActivity.ARG_AUTH_TYPE, authTokenType); final Bundle bundle = new Bundle(); bundle.putParcelable(AccountManager.KEY_INTENT, intent); return bundle; } 28 @tsmith
29. AccountAuthenticatorActivity Success private void finishLogin(String accountName, String accountType, String password, String authToken, String authTokenType) { Account account = new Account(accountName, accountType); if (getIntent().getBooleanExtra(ARG_IS_ADDING_NEW_ACCOUNT, false)) { accountManager.addAccountExplicitly(account, password, null); } accountManager.setPassword(account, password); accountManager.setAuthToken(account, authTokenType, authToken); Intent intent = new Intent(); intent.putExtra(AccountManager.KEY_ACCOUNT_NAME, userName); intent.putExtra(AccountManager.KEY_ACCOUNT_TYPE, ACCOUNT_TYPE); intent.putExtra(AccountManager.KEY_AUTHTOKEN, authToken); setAccountAuthenticatorResult(intent.getExtras()); setResult(RESULT_OK, intent); finish(); } 29 @tsmith
30. Sync Adapter • Sync App and Web Service • User visible syncing • Network/battery optimized • Provided to third party apps • Schedule and GCM 30 @tsmith
31. Sync Adapter public class ImagesSyncAdapter extends AbstractThreadedSyncAdapter { private final AccountManager accountManager; public TvShowsSyncAdapter(Context context, boolean autoInitialize) { super(context, autoInitialize); accountManager = AccountManager.get(context); } @Override public void onPerformSync(Account account, Bundle extras, String authority, ContentProviderClient provider, SyncResult syncResult) { String authToken = accountManager.blockingGetAuthToken(account, AccountGeneral.AUTHTOKEN_TYPE_FULL_ACCESS, true); List<Images> images = getImagesFromServer(authToken); updateImagesOnDisk(provider, images); } } 31 @tsmith
32. Sync Adapter public class ImagesSyncService extends Service { private static final Object syncAdapterLock = new Object(); private static ImagesSyncAdapter syncAdapter = null; @Override public void onCreate() { synchronized (syncAdapterLock) { if (syncAdapter == null) syncAdapter = new ImagesSyncAdapter(getApplicationContext(), true); } } @Override public IBinder onBind(Intent intent) { return syncAdapter.getSyncAdapterBinder(); } } 32 @tsmith
33. Sync Adapter res/xml/sync_adapter.xml <sync-adapter xmlns:android="http://schemas.android.com/apk/res/android" android:contentAuthority="com.example.images.provider" android:accountType="com.example.sync_example" android:userVisible="true" android:allowParallelSyncs="false" android:isAlwaysSyncable="false" android:supportsUploading="true"/> 33 @tsmith
34. Sync Adapter AndroidManifest.xml <service android:name=".syncadapter.ImagesSyncService" android:exported="true"> <intent-filter> <action android:name="android.content.SyncAdapter" /> </intent-filter> <meta-data android:name="android.content.SyncAdapter" android:resource="@xml/sync_adapter" /> </service> 34 @tsmith
35. Sync Adapter Sync Every Hour int interval = 3600; ContentResolver.addPeriodicSync(account, AppContract.AUTHORITY, new Bundle(), interval); 35 @tsmith
36. Sync Adapter Jitter int jitteredInterval = 3600 + new Random().nextInt(300); ContentResolver.addPeriodicSync(account, AppContract.AUTHORITY, new Bundle(), jitteredInterval); 36 @tsmith
37. Binding Services for IPC • Android Interface Definition Language (AIDL) • Communicate between process or app • Directly call defined RPC methods • Requires consumer to contain interface 37 @tsmith
38. Binding Services Create AIDL interface RemoteMessageService { void passMessage(String "message"); } 38 @tsmith
39. Binding Services Implement AIDL public class MessageBinder implements RemoteMessageService.Stub() { public void passMessage(String message) { Log.d(TAG, message); } } 39 @tsmith
40. Binding Services Expose Interface public class RemoteService extends Service { @Override public IBinder onBind(Intent intent) { return new MessageBinder; } } 40 @tsmith
41. Binding Services Connecting private ServiceConnection connection = new ServiceConnection() { public void onServiceConnected(ComponentName className, IBinder service) { service = IRemoteService.Stub.asInterface(service); } public void onServiceDisconnected(ComponentName className) { service = null; } } public void onResume() { bindService(new Intent(this, RemoteMessageService.class), connection, Context.BIND_AUTO_CREATE); } public void onPause() { unbindService(connection); service = null; } 41 @tsmith
42. Permissions • Inform the User • Mitigate Exploits 42 @tsmith
43. Permissions Levels • Normal • Dangerous • Signature • SignatureOrSystem 43 @tsmith
44. Permissions Custom <permission android:name="com.example.perm.READ" android:label="@string/permission_label" android:description="@string/permission_description" android.protectionLevel="dangerous" android:permissionGroup="com.example.permission-group.MYAPP_DATA" /> • Can be used to restrict access to various services and components • Required to interact with app that declares it • Can be checked programatically or via Manifest. 44 @tsmith
45. Permissions Enforcing Programitcally int canProcess = getContext().checkCallingPermission("com.example.perm.READ"); if (canProcess != PERMISSION_GRANTED) { throw new SecurityException("Requires Custom Permission"); } • checkCallingOrSelfPermission() can leak permissions 45 @tsmith
46. Permissions Enforcing via XML <permission android:name="com.example.perm.READ" android:permissionGroup="com.example.permission-group.MYAPP_DATA" android:protectionLevel="dangerous" /> <permission android:name="myapp.permission.WRITE" android:permissionGroup="com.example.permission-group.MYAPP_DATA" android:protectionLevel="dangerous" /> <provider android:name=".data.DataProvider" android:exported="true" android:authorities="com.example.data.DataProvider" android:readPermission="com.example.perm.READ" android:writePermission="com.example.perm.WRITE" /> 46 @tsmith
47. Debugging Tips • Debugging app integrations is hard • Logging is your friend • Test with mock integrations • Communicate your data contracts • Seek User Feedback • Analytics and Crash Reporting 47 @tsmith
48. Integration Requirements • Get Note(s) (Intent & Content Provider) • List Notes (Intent) • Create/Update Notes (Intent & Content Provider) • Delete Notes (Intent & Content Provider) • Account Sync (Account Manager & Sync Adapter) • Get Preferences (Content Provider and bound Services) 48 @tsmith
49. Resources Example App Dashclock for Evernote Android Developer Docs on AIDL Write your own Android Authenticator 49 @tsmith
50. Thanks! Ty Smith @tsmith 50 @tsmith