1. Alex Yanchenko @ de.droidcon.com/2014
DroidParts Explained

2. ●
SQL operations.
●
JSON (de)serialization.
●
HTTP interactions.
●
Loading, caching, displaying images.
●
Performing work in background.
●
Logging.
●
Dependency management.
●
Publish/subscribe (aka Event Bus).
●
Misc repeating tasks.
Common Tasks

3. Existing Solutions
Cursor query(boolean distinct, String table, String[]
columns, String selection, String[]
selectionArgs, String groupBy, String having,
String orderBy, String limit);
static final String TAG = InEvery.class.getSimpleName();
Log.wtf(TAG, "Y TAG?!");
Picasso.with(context).load(url).placeholder(R.drawable.ph)
.error(R.drawable.err).into(imageView);
Repetetive code:
Not using a builder when should:
Using a builder when shouldn't:
(Fluent kills inheritance)

4. Existing Solutions
Gson gson = new GsonBuilder().excludeFieldsWithModifiers(
Modifier.STATIC).create();
// By default, if you mark a field as transient, it will be
excluded.
The @DatabaseField annotation can have the following fields:
(27 ot them)
Entity user = schema.addEntity("User");
user.addIdProperty();
user.addStringProperty("name");
user.implementsSerializable();
// Then generate .java files & paste to your project.
A mess to maintain:
Abusing built-in language features:
Many features remain unused on mobile:

5. Existing Solutions
<com.android.volley.toolbox.NetworkImageView
android:id="@+id/pic" />
NetworkImageView pic = (NetworkImageView)view
.findViewById(R.id.pic);
pic.setImageUrl("http://example.com/pic.png",
mImageLoader); // OMG
AsyncHttpClient client = new AsyncHttpClient();
client.get("http://example.com/timeline.json", new
JsonHttpResponseHandler() {
@Override
public void onSuccess(JSONArray response) {
System.out.println(
"Keep calm & process JSON on the UI thread.");
}
});
Ignoring separation of concerns #2:
Ignoring separation of concerns:

6. Existing Solutions
Coded past “Ballmer Peak”:
@Headers({
"Accept: application/vnd.github.v3.full+json",
"User-Agent: Retrofit-Sample-App"
})
@GET("/group/{id}/users")
List<User> groupList(@Path("id") int groupId,
@QueryMap Map<String, String> options);
©xkcd

7. ●
Help handle most common tasks?
●
Uniform API?
●
Simple to make easy things easy?
●
Flexible to make hard things possible?
●
Won't reinvent Java, OO friendly?
●
Like Django, but for Android?
What If?

8. Yes.
What If?

9. ●
Dependency Inection.
●
EventBus.
●
JSON (de)serialization.
●
Object-Relational Mapping.
●
AsyncTask, IntentService.
●
RESTClient.
●
ImageFetcher.
●
Logger.
●
Misc.
DroidParts Parts
250kB, 8kLOC (v.2.0.4)

10. App Blocks
HTTP/REST JSON SQL/ORM
IntentService
Activity
Fragment
View
AsyncTask
EventBus
Dependency
Injection

11. AndroidManifest.xml:
DI Setup
<meta-data
android:name="droidparts_dependency_provider"
android:value=".DependencyProvider" />
public class DependencyProvider extends
AbstractDependencyProvider {
public DependencyProvider(Context ctx) {
super(ctx);
}
}
DependencyProvider.java:

12. DependencyProvider
private final DBOpenHelper dbOpenHelper;
private PrefsManager prefsManager;
public DependencyProvider(Context ctx) {
super(ctx);
dbOpenHelper = new DBOpenHelper(ctx);
}
@Override
public AbstractDBOpenHelper getDBOpenHelper() {
return dbOpenHelper;
}
public PrefsManager getPrefsManager(Context ctx) {
if (prefsManager == null) {
prefsManager = new PrefsManager(ctx);
}
return prefsManager;
}
public DialogFactory getDialogFactory(Context ctx) {
return new DialogFactory(ctx);
}

13. Injection Annotations
@InjectDependency - from DependencyProvider
@InjectParentActivity - in a Fragment
@InjectView(int id, boolean click) - from layout
@InjectFragment(int id) - in an Activity
@InjectResource(int value) - strings, images...
@InjectSystemService - TelephonyManager, ...
@InjectBundleExtra(String key, boolean optional)
- from Intent in an Activity
or from args in a Fragment

14. Injection in an Activity
class MyActivity extends Activity implements OnClickListener {
@InjectSystemService
private LayoutInflater layoutInflater;
@InjectDependency
private DialogFactory dialogFactory;
@InjectView(id = R.id.button_add, click = true)
private Button addButton;
@Override
public void onPreInject() {
setContentView(R.layout.activity_my);
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState); // <-- Injection
}
@Override
public void onClick(View v) {
if (v == addButton) { // TODO }
}
}

15. Base Activities
class MyActivity extends Activity {
@Override
public void onPreInject() {
setContentView(R.layout.activity_my);
}
}
package org.droidparts.activity;
class Activity extends android.app.Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
onPreInject();
Injector.inject(this); // <-- Magic
}
}
App Activity:
DroidParts Activity:

16. Base Activities & Fragments
DroidParts:
●
3.0+ with ActionBar features
●
Pre-3.0, no ActionBar
(.legacy.*)
DroidParts Support:
●
Pre-3.0 with Android Support Library
(.support.v4.*)
●
Pre-3.0 with ActionBarSherlock
(.sherlock.*)
●
Pre-3.0 with Android Support Library ActionBar
(.support.v7.*)

17. Base Activities & Fragments
No “DroidParts” or “DP” prefix.
Nice features:
→
SingleFragmentActivity
TabbedFragmentActivity

18. Activity Factory Methods
class PostListActivity extends Activity {
private static final String EXTRA_POSTS = "posts";
public static Intent getIntent(Context ctx,
ArrayList<Post> posts) {
Intent intent = new Intent(ctx, MyActivity.class);
intent.putExtra(EXTRA_POSTS, posts);
return intent;
}
@InjectBundleExtra(key = EXTRA_POSTS)
private ArrayList<Post> posts;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// TODO display posts.
}
}

19. Fragment Listener
class PostListActivity extends Activity
implements PostListFragment.Listener {
@InjectFragment
private PostListFragment fragment;
@Override
public void onPreInject() {
setContentView(R.layout.layout_with_fragments);
}
}
class PostListFragment extends ListFragment {
public interface Listener {
void doShowImageDetail(int position);
}
@InjectParentActivity
private Listener listener;
}

20. EventBus
(aka MessageBus)
●
Message: Name + optional payload Object.
(not a custom class)
●
Sent from any thread, delivered on the UI thread.

21. EventBus
interface EventReceiver<T> {
void onEvent(String name, T data);
}
EventBus.postEvent(String name)
// or
EventBus.postEventSticky(String name, Object data)
Send:
Receive:
EventBus.registerReceiver(EventReceiver<T> receiver,
String... eventNames)
// TODO Remember to unregister.

22. EventBus
@ReceiveEvents(name = { "MESSAGE_SENT", "MESSAGE_RECEIVED" })
private void onMessageEvent(String eventName) {
// TODO process 2 types of events without data
}
@ReceiveEvents
private void onAnyEvent(String eventName, Object eventData) {
// TODO process any event with optional data
}
EventBus.postEvent(String name)
// or
EventBus.postEventSticky(String name, Object data)
Send:
Receive in an injected class:

23. Data Layer
JSON ORM
IntentService AsyncTask

24. JSON, ORM
// JSON
class JSONSerializer<ModelType extends Model> {}
// ORM
class EntityManager<EntityType extends Entity> {}
// JSON
class Model implements Serializable {}
// ORM
class Entity extends Model {
@Column(name = "_id")
public long id;
}
Base Model Classes:
Managers:

25. JSON
@Key(Sting name, boolean optional)
Using org.json.* under the hood.
class JSONSerializer<ModelType extends Model> {
JSONObject serialize(ModelType item)
JSONArray serialize(Collection<ModelType> items)
ModelType deserialize(JSONObject obj)
ArrayList<ModelType> deserialize(JSONArray arr)
}
Annotation:
Manager:

26. JSON
{
"author": "Alex"
"address": "http://droidparts.org",
"posts": [{
"published": 1398970584375,
"title": "Title",
}],
}
class Blog extends Model {
@Key
public String author;
@Key(name="address")
public Uri uri;
@Key
public Post[] posts;
}
class Post extends Model {
@Key
public Date published;
@Key(name="title", optional=false)
public String title;
@Key(optional = true)
public String text = "";
}

27. JSON
{
"sub_obj": {
"str": "val"
}
}
@Key(name = "sub_obj" + Key.SUB + "str")
String str;
@Override
public Blog deserialize(JSONObject obj) throws JSONException {
Blog blog = super.deserialize(obj);
for (Post post : blog.posts) {
post.blog = blog;
}
return blog;
}
Override serialize()/deserialize() for tweaking:
Accessing nested object's property:

28. ORM
@Table(name = "posts")
public class Post extends Entity {
@Column
public Date published;
@Column(unique = true)
public String title;
@Column(nullable = true)
public String text = "";
@Column(eager = true)
public Blog blog;
}
@Table(String name)
@Column(String name, boolean nullable, boolean unique,
boolean eager)
Annotations:
Class example:

29. ORM
class Blog extends Entity {
List<Post> getPosts() {
EntityManager<Post> em = new EntityManager<Post>(
Post.class,
Injector.getApplicationContext());
Select<Post> select = em.select().where("blog_id",
Is.EQUAL, this.id);
return em.readAll(select);
}
}
Reading one-to-many:

30. EntityManager: C_UD
class Post extends Entity {}
EntityManager<Post> em =
new EntityManager<Post>(Post.class, ctx);
// Usually subclass & add helper methods.
Post post = new Post();
em.create(post);
assert(post.id != 0);
em.update(post);
em.createOrUpdate(post);
int postsDeleted = em.delete()
.where("year", Is.LESS, 2013)
.execute();

31. EntityManager: _R__
EntityManager<Post> em;
// 1
Select<Post> select = em.select().columns("_id", "name").
where("blog_id", Is.EQUAL, 10);
// 2
Where haveCoordinaltes = new Where("latitude", Is.NOT_EQUAL,
0).or("longitude", Is.NOT_EQUAL, 0);
em.select().where("country", Is.EQUAL, "us").where(
haveCoordinates);
// 3
Cursor cursor = em.select().where("author", Is.LIKE, "%%alex%%").
execute();
Select:

32. DB Contract
interface DB {
interface Table {
}
interface Column {
String ID = BaseColumns._ID;
}
}
@Table(name = DB.Table.BLOGS)
class Blog extends Entity {
@Column(name = DB.Column.NAME, unique = true)
String name;
}
import static org.exapmpe.app.DB.Column.*;
em.select().columns(ID, NAME).where(BLOG_ID, Is.EQUAL, 10);

33. DBOpenHelper
package org.droidparts.persist.sql;
class AbstractDBOpenHelper extends SQLiteOpenHelper { }
class DBOpenHelper extends AbstractDBOpenHelper {
@Override
protected void onCreateTables(SQLiteDatabase db) {
createTables(db, Blog.class, Post.class);
createIndex(db, "blogs", false, "title");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion,
int newVersion) {
addMissingColumns(db, Blog.class, Post.class)
}
}

34. EntityCursorAdapter
class PostListAdapter extends EntityCursorAdapter<Post> {
PostListAdapter(Context ctx, Select<Post> select) {
super(ctx, Post.class, select);
}
@Override
void bindView(Context context, View view, Post item) {
//TODO
}
}
Select object:
●
Has type information.
●
Can read an instance.
●
Wraps a Cursor.
●
Perfect data source for an Adapter.

35. ViewHolder
class ViewHolder {
public ViewHolder(View view) {
Injector.inject(view, this);
}
}
View view = layoutInflater.inflate(android.R.layout.
simple_list_item_1);
Text1Holder holder = new Text1Holder(view);
view.setTag(holder);
holder.text1.setText("Text 1");
class Text1Holder extends ViewHolder {
@InjectView(id = android.R.id.text1)
public TextView text1;
public Text1Holder(View view) {
super(view);
}
}

36. JSON, ORM
Supported types:
●
Primitives, wrapper classes.
●
Enums
●
JSONObject, JSONArray
●
Uri
●
UUID
●
Drawables
●
Models (JSON only), Entities
●
Arrays & collections

37. JSON, ORM
public class MyClassConverter extends Converter<MyClass> {
@Override
public boolean canHandle(Class<?> cls) { // TODO }
@Override
public String getDBColumnType() { // TODO }
@Override
public <V> MyClass readFromJSON(Class<MyClass> valType,
Class<V> componentType, JSONObject obj,
String key) throws JSONException { // TODO }
@Override
public <V> void putToContentValues(Class<MyClass> valueType,
Class<V> componentType, ContentValues cv,
String key, MyClass val) { // TODO }
// ...
}
ConverterRegistry.registerConverter(new MyClassConverter());
Adding new type support:

38. Background Work
AsyncTask:
●
Ad-hoc tasks, based on user input.
●
Important if succeeded.
●
Independent, non-cancellable.
●
Submitting a post.
IntentService:
●
Regular tasks, scheduled.
●
Not important if succeeded.
●
Sequential, cancellable.
●
Querying for new comments.

39. AsyncTask
class AsyncTask<Params, Progress, Result> extends
android.os.AsyncTask<...> {
abstract Result onExecute(Params... params) throws
Exception;
}
interface AsyncTaskResultListener<Result> {
void onAsyncTaskSuccess(Result result);
void onAsyncTaskFailure(Exception e);
}
AsyncTaskListener:
AsyncTask:
SimpleAsyncTask:
class SimpleAsyncTask<Result> extends
AsyncTask<Void, Integer, Result> {
abstract Result onExecute() throws Exception;
}

40. IntentService
abstract Bundle onExecute(String action, Bundle data)
throws Exception;
static Intent getIntent(Context ctx, Class<? extends
IntentService> cls, String action)
static Intent getIntent(Context ctx, Class<? extends
IntentService> cls, String action,
ResultReceiver resultReceiver)
public static final int RESULT_SUCCESS = Activity.RESULT_OK;
public static final int RESULT_FAILURE = Activity.
RESULT_CANCELED;
//
public static final String EXTRA_ACTION = "__action__";
public static final String EXTRA_EXCEPTION = "__exception__";
void removePendingIntents()
class IntentService extends android.app.IntentService {}

41. Networking Layer
RESTClient
ImageFetcher

42. RESTClient
●
GET, PUT, POST, DELETE
●
Uses gzip|deflate compression.
●
Supports in and out headers.
●
Transparent cookies support.
●
Http basic auth.
●
ETag & If-Modified-Since support.
●
Getting response as String or InputStream.
●
POST multipart file.
●
HttpURLConnection, Apache HTTP Client,
OkHttp workers.

43. RestClient
RESTClient(Context ctx)
RESTClient(Context ctx, String userAgent)
RESTClient(Context ctx, HTTPWorker worker)
RESTClient client = new RESTClient(ctx);
client.authenticateBasic("user", "pass");
client.setHeader("X-Header", "Val");
try {
HTTPResponse resp = client.get("http://example.
com/endpoint");
client.post("http://example.com/endpoint", "text/plain",
"txt");
} catch (HTTPException e) { // TODO }
class HTTPResponse {
public int code;
public Map<String, List<String>> headers;
public String body;
// or
public HTTPInputStream inputStream;
}

44. RestClient2
try {
RESTClient2 client = new RESTClient2(ctx);
JSONObject obj = client.getJSONObject("http://example.
com/endpoint");
JSONArray arr;
client.put("http://example.com/endpoint", arr);
} catch (HTTPException e) { // TODO }
Adds JSON support.
class HTTPException extends Exception {
public HTTPException(int respCode, String respBody) {
super(respBody);
this.respCode = respCode;
}
public int getResponseCode() {
return respCode;
}
}

45. Data + Network Layers
JSON ORM
IntentService AsyncTask
RESTClient

46. ImageFetcher
class ImageFetcher {
ImageFetcher(Context ctx) {
this(ctx,
new BackgroundThreadExecutor(2, "ImageFetcher-Fetch"),
new RESTClient(ctx),
BitmapMemoryCache.getDefaultInstance(ctx),
BitmapDiskCache.getDefaultInstance(ctx));
}
}
void attachImage(String imgUrl, ImageView imageView)
// ...
void attachImage(String imgUrl,
ImageView imageView,
ImageReshaper reshaper,
int crossFadeMillis,
ImageFetchListener listener,
Bitmap inBitmap)

47. ImageFetcher
interface ImageReshaper {
String getCacheId();
Pair<CompressFormat, Integer> getCacheFormat(String
mimeType);
Bitmap.Config getBitmapConfig();
int getImageWidthHint();
int getImageHeightHint();
Bitmap reshape(Bitmap bm);
}
abstract class AbstractImageReshaper implements ImageReshaper {
// TODO Check it out.
}

48. ImageFetcher
interface ImageFetchListener {
void onFetchAdded(ImageView imageView, String imgUrl);
void onFetchProgressChanged(ImageView imageView, String
imgUrl,
int kBTotal, int kBReceived);
void onFetchFailed(ImageView imageView, String imgUrl,
Exception e);
void onFetchCompleted(ImageView imageView, String imgUrl,
Bitmap bm);
}

49. L(ogger)
AndroidManifest.xml:
<meta-data
android:name="droidparts_log_level"
android:value="warn" />
Object anyObj;
L.w(anyObj);
long time = System.currentTimeMillis() - start;
L.wtf("Took %dms.", time);
DependencyProvider.<init>():39: Took 10ms.
DependencyProvider: Took 10ms.
Development mode:
Signed app:

50. See in action in
DroidPartsGram
droidparts-samples/
DroidPartsGram