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
   

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3. 3 @tsmith
   

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4. 4 @tsmith
   

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5. Integration Requirements
   • Get Note(s)
   • List Notes
   • Create/Update Notes
   • Delete Notes
   • Account Sync
   • Get Preferences
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6. Android Components Needed
   1. Intents
   2. Content Provider
   3. Account Manager
   4. Sync Adapter
   5. Inter Process Communication
   6. Permissions
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7. Intents
   Overview
   • Simple message between two components
   • Bundle - key/value data
   • Limited payload size (1MB)
   • Inefficient for batch operations
   • Defined Action
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8. Intents
   Standard Actions
   • ACTION_SEND
   • ACTION_SEND_MULTIPLE
   • ACTION_VIEW
   • ACTION_EDIT
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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);
   }
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10. Editing Intent
    Receiver
    
    
    
    
    
    
    
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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();
    }
    }
    }
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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
    }
    }
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13. Intents
    Edit Caveats
    • Use copy of file
    • Don’t rely on setResult()
    • Use a ContentObserver
    • Check for file modified
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14. Intents
    Custom Actions
    com.example.action.note.*
    list - view - new - create
    edit - update - delete
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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);
    }
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16. Content Provider
    A well defined database access layer
    • SQLite
    • Interact with large volumes of data
    • Authority
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17. Content Provider
    URI
    content:// com.example / users / 1
    Scheme Authority Data Id
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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
    

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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);
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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);
    }
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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!
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22. Account Manager
    • Accessible Account
    • Authentication Token
    • Consistency
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23. Providing your own Accounts
    • AbstractAccountAuthenticator
    • AccountAuthenticatorActivity
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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;
    }
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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);
    }
    }
    ...
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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;
    }
    ...
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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;
    }
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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
    

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30. Sync Adapter
    • Sync App and Web Service
    • User visible syncing
    • Network/battery optimized
    • Provided to third party apps
    • Schedule and GCM
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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 = getImagesFromServer(authToken);
    updateImagesOnDisk(provider, images);
    }
    }
    31 @tsmith
    

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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
    

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33. Sync Adapter
    res/xml/sync_adapter.xml
    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
    

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34. Sync Adapter
    AndroidManifest.xml
    android:name=".syncadapter.ImagesSyncService"
    android:exported="true">
    
    
    
    android:name="android.content.SyncAdapter"
    android:resource="@xml/sync_adapter" />
    
    34 @tsmith
    

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35. Sync Adapter
    Sync Every Hour
    int interval = 3600;
    ContentResolver.addPeriodicSync(account,
    AppContract.AUTHORITY,
    new Bundle(),
    interval);
    35 @tsmith
    

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36. Sync Adapter
    Jitter
    int jitteredInterval = 3600 + new Random().nextInt(300);
    ContentResolver.addPeriodicSync(account,
    AppContract.AUTHORITY,
    new Bundle(),
    jitteredInterval);
    36 @tsmith
    

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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
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38. Binding Services
    Create AIDL
    interface RemoteMessageService {
    void passMessage(String "message");
    }
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39. Binding Services
    Implement AIDL
    public class MessageBinder implements RemoteMessageService.Stub() {
    public void passMessage(String message) {
    Log.d(TAG, message);
    }
    }
    39 @tsmith
    

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40. Binding Services
    Expose Interface
    public class RemoteService extends Service {
    @Override
    public IBinder onBind(Intent intent) {
    return new MessageBinder;
    }
    }
    40 @tsmith
    

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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
    

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42. Permissions
    • Inform the User
    • Mitigate Exploits
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43. Permissions
    Levels
    • Normal
    • Dangerous
    • Signature
    • SignatureOrSystem
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44. Permissions
    Custom
    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
    

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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
    

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46. Permissions
    Enforcing via XML
    android:permissionGroup="com.example.permission-group.MYAPP_DATA"
    android:protectionLevel="dangerous" />
    android:permissionGroup="com.example.permission-group.MYAPP_DATA"
    android:protectionLevel="dangerous" />
    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
    

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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
    

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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
    

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49. Resources
    Example App
    Dashclock for Evernote
    Android Developer Docs on AIDL
    Write your own Android Authenticator
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50. Thanks!
    Ty Smith
    @tsmith
    50 @tsmith
    

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