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ActionChain

Circle CI

A substitute for AsyncTask. Also a "variant" of JDeferred where you could easily specify the thread to run actions on. For type-safe ActionChains, please refer to TActionChain class, and TActionChainTest

Sample Code :)

Example 0:

The original AsyncTask version of code was created by Graham Smith on Stack Overflow.

public class AsyncTaskActivity extends Activity implements OnClickListener {

    Button btn;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        btn = (Button) findViewById(R.id.button1);
        btn.setOnClickListener(new View.OnClickListener()
        {
            @Override
            public void onClick(View view)
            {
                new LongOperation().execute("");
            }
        });
    }

    private class LongOperation extends AsyncTask<String, Void, String> {

        @Override
        protected String doInBackground(String... params) {
			// TODO: replace this with real network, blocking actions
            for (int i = 0; i < 5; i++) {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    Thread.interrupted();
                }
            }
            return "Executed";
        }

        @Override
        protected void onPostExecute(String result) {
            TextView txt = (TextView) findViewById(R.id.output);
            txt.setText("Executed"); // txt.setText(result);
            // might want to change "executed" for the returned string passed
            // into onPostExecute() but that is upto you
        }

        @Override
        protected void onPreExecute() {}

        @Override
        protected void onProgressUpdate(Void... values) {}
    }
}

The basic idea is to avoid instantiating abstract classes, which are too lengthy code. And the tool to partially accomplish this goal is the new feature brought in Java 8 -- lambda. (In Java 7, we could get lambda support using RetroLambda.)

Basically as long as the abstract class has only one abstract method it could be shortened like this:

The original code:

        btn = (Button) findViewById(R.id.button1);
        btn.setOnClickListener(new View.OnClickListener()
        {
            @Override
            public void onClick(View view)
            {
                new LongOperation().execute("");
            }
        });

The simplified code using Java 8 or Retrolambda:

        btn = (Button) findViewById(R.id.button1);
        btn.setOnClickListener(view -> new LongOperation().execute(""));

This convertion is available for .setOnClickListener because the abstract class only needs one function. However AsyncTask could not be directly shortened as a simple Lambda because it needs 4 functions, all of which are important and cannot be ignored, too.

Therefore we need a new interface similar to AsyncTask that helps building something similar while enabling developers to use lambdas. And the new interface, ActionChain looks like this:

public class AsyncTaskActivity extends Activity implements OnClickListener {

    Button btn;

    // create a ActionChain factory using Android API (runOnUiThread) and 2 extra worker threads.
    ActionChainFactory chainFactory = new ActionChainFactory(uiCode -> runOnUiThread(uiCode), Executors.newFixedThreadPool(2));
    TextView txt;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        txt = (TextView) findViewById(R.id.output);
        btn = (Button) findViewById(R.id.button1);
        btn.setOnClickListener(view -> onBtnClick());
    }

    void onBtnClick() {
        // The following code is using ActionChain
        // The ").xxx" style may look strange but that's the only way to obey most IDEs' indentation rule.

        chainFactory.get(
        ).uiConsume(obj -> {                                // equivalent to onPreExecute, could be deleted
        }).netThen(obj -> {                                 // equivalent to doInBackground
			// TODO: replace this with real network, blocking actions
            for(int i = 0; i < 5; i++) {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    Thread.interrupted();
                }
            }
            return "Executed";
        }).uiConsume((String result) -> txt.setText(result)    // equivalent to onPostExecute
        ).start();
    }
}

The different between "xxConsume" and "xxThen" is that "Consume" will not return new values to the chain and set the chain's inner value to "null" but "Then" will return a value and pass that value to inner chain value, so the next "Then" or "Consume" will receive that value as input parameter.

Example 1:

Realm database caused some trouble for us because it's required to be run on the same thread and defaults to run on UI thread, which might affect user experience. But ActionChain enables you to restrict Realm to run only on worker threads, in a simple yet safe way:

Encapsulation of Realm
/**
 * Created on 3/14/16 
 *
 * Note: PureAction<I,O> is interface for a function that takes an argument of type I and returns an object of type O
 *       ReadOnlyChain is the object representing a launched ActionChain.
 *       (ActionChain is not launched until calling ".start()")
 */
public class RealmAccess implements PureAction<PureAction<Realm, ?>, ReadOnlyChain> {

    @Inject
    ActionChainFactory chainFactory;

    @Inject
    Context context;

    @Override
    public ReadOnlyChain process(PureAction<Realm, ?> editor) throws Exception {
        return chainFactory.get(fail -> fail.getCause().printStackTrace()
        ).netThen(() -> {
            Realm realm = Realm.getInstance(new RealmConfiguration.Builder(context)
                    .name(context.getString(R.string.realm_filename))
                    .deleteRealmIfMigrationNeeded()
                    .build());
            Object result = editor.process(realm);
            realm.close();
            return result;
        }).start();
    }
}
Usage of ReamAccess

Example 1.1:

// Retrieve current user
chainFactory.get(fail -> fail.getCause().printStackTrace()
).netThen(() -> realmAccess.process(realm -> {
    return realm.where(Person.class)
            .equalTo("personId", userStore.getMostRecentUserId())
            .findFirst().getName();
})).uiConsume((String name) -> {
    mUserName.setText(name);
}).start();

Example 1.2:

chain.netThen((String userName) -> {
    Response<ResponseBody> response = service.getCurrentPerson().execute();
    Person person = new Person();
    if (response.code() != 200)
        throw new IOException(response.message());
    ResponseBody responseBody = response.body();
    JSONObject jsonObject = new JSONObject(responseBody.string());

    String ourUserID = jsonObject.getString("_id");

    // Set user ID in preferences
    userStore.setUserId(ourUserID);

    Photo photo = new Photo();
    photo.setPhotoUrl(jsonObject.getString("avatarUrl"));
    photo.setType(Photo.TYPE_AVATAR);
    person.setName(userName);
    person.setAvatar(photo);
    person.setFacebookId(jsonObject.getString("facebookId"));
    person.setCreatedAt(DateTimeConverter.toDate(jsonObject.getString("createdAt")));
    person.setPersonId(ourUserID);

    Log.d("UpUserInfo", "A" + person);

    return person;
}).netThen((Person newPerson) -> realmAccess.process(realm -> {
    try {
        Log.d("UpUserInfo", newPerson == null ? "null" : newPerson.toString());
        // Set user details in database
        realm.beginTransaction();
        Person result = realm.where(Person.class)
                .equalTo("personId", newPerson.getPersonId())
                .findFirst();
        if (result != null)
            result.removeFromRealm();
        realm.copyToRealm(newPerson);
        realm.commitTransaction();
        // MAYBE NOT NEEDED: bus.post(new UserInfoUpdatedEvent(result));
        return newPerson;
    } catch (Exception err) {
        // Maybe errorHolder.retry() ?

        if (realm.isInTransaction())
            realm.cancelTransaction();
        err.printStackTrace();
        throw err;
    }
}));

Example 2

Android application, used with retrolambda

AsyncTask version

Untangled version:

  1. Creating and using action chain
  2. Creating a set of actions for .use()
  • Althought the event bus version also eliminates callback hell, AsyncTask forces developers to think in a un-natural way, where:
    • UI code and other operations cannot be mixed together. (Otherwise the code will contain lots of small pieces of AsyncTasks)
    • It's not straightforward to understand the sequence of the Tasks
  • ActionChain Bonus:
    • Once-for-all exception handling for all the threads, as long as they are in the same task.

Diagram illustration

We turn this tangled thought:

#### into this linear, straightforward one:

Documentations

Please visit this github.io website.

It's recommended to begin by reading the documentations about ChainStyle and ErrorHolder.

Get Started

Thanks to JitPack, we could all import this library using standard syntax!

For gradle:

1. Add the JitPack repository (please edit /build.gradle)
allprojects {
    repositories {
        ...
        maven { url "https://jitpack.io" }
    }
}
2. Add the dependency (please edit /<module name>/build.gradle)
dependencies {
  compile 'com.github.C4Phone:SmartActionChain:v0.3'
}

For Maven:

1. Add the JitPack repository
    <repositories>
        <repository>
            <id>jitpack.io</id>
            <url>https://jitpack.io</url>
        </repository>
    </repositories>
2. Add the dependency
    <dependency>
        <groupId>com.github.C4Phone</groupId>
        <artifactId>SmartActionChain</artifactId>
        <version>v0.3</version>
    </dependency>