DroidParts is a library that helps handle common tasks in Android development such as: - SQL operations, JSON serialization/deserialization, HTTP interactions, loading and caching images, background processing, logging, and dependency injection. It provides solutions for these tasks through modular "parts" including an ORM, JSON serializer, REST client, image fetcher, logger, and more. The library aims to provide a simple yet flexible API and avoid reimplementing core Java and OO principles.

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