State Machine for Android

A lightweight state machine implementation for Android.

Download

Via gradle. In main build.gradle :

allprojects {
    repositories {
        ...
        maven {
            url "https://oss.sonatype.org/content/repositories/snapshots"
        }
    }
}

Add library:

compile 'com.polidea:statemachine:1.0.0-SNAPSHOT'

or Maven. Add plugin repository:

<pluginRepository>
    <url>https://oss.sonatype.org/content/repositories/snapshots/</url>
    <snapshots>
        <enabled>true</enabled>
    </snapshots>
</pluginRepository>

Add library:

<dependency>
  <groupId>com.polidea</groupId>
  <artifactId>statemachine</artifactId>
  <version>1.0.0-SNAPSHOT</version>
</dependency>

It is a stable version of library

Usage

Creating custom BaseStateableHandler

The easiest way to use StateMachine is to extend BaseStateableHandler. It have 4 main methods that we should override:

• getStateProvider() - used by State's to get data from our Fragment/Activity. Base StateProvider contains one method provideContext()
• getActionInterface() - used by State's to perform action's on Activity/Fragment, e.g. show Toast.
• getInitialStateClass() - initial state class for StateMachine. By default it returns InitialState class.
• onStateMachineDescribe(StateMachine stateMachine) - here we should describe transitions between states in our StateMachine. Each transition is a set of: from class, to class, event id. It means: when current state is 'from state' and it will propagate 'event id' then state machine should go to 'to state'.

Sample BaseStateableHandler:

public class LoginStateableHandler extends BaseStateableHandler<LoginProvider, LoginActionInterface> implements LoginProvider, LoginActionInterface {
    @Override
    public LoginProvider getStateProvider() {
        return this;
    }

    @Override
    public LoginActionInterface getActionInterface() {
        return this;
    }

    @Override
    public int provideFragmentContainerId() {
        return R.id.fragment_container;
    }

    @Override
    public void onStateMachineDescribe(StateMachine<LoginProvider, LoginActionInterface> stateMachine) {
        stateMachine.addTransitionFromClass(LoginInitialState.class, LoginEvents.START_LOGIN, OnGoingLoginState.class);

        stateMachine.addTransitionFromClass(OnGoingLoginState.class, LoginEvents.CANCELLED, LoginInitialState.class);
        stateMachine.addTransitionFromClass(OnGoingLoginState.class, LoginEvents.SENDING_IN_PROGRESS, WaitingForLoginRequestState.class);

        stateMachine.addTransitionFromClass(WaitingForLoginRequestState.class, LoginEvents.FINISHED, InitialState.class);
    }

    @Override
    public Class<? extends State> getInitialStateClass() {
        return LoginInitialState.class;
    }

    ...
}

As you can see here, state machine contains 3 states: LoginInitialState, OnGoingLoginState and WaitingForLoginRequestState. Initial state is LoginInitialState. Looking at one of transition:

stateMachine.addTransitionFromClass(LoginInitialState.class, LoginEvents.START_LOGIN, OnGoingLoginState.class);

means that, when state machine is in LoginInitialState and that state will fire LoginEvents.START_LOGIN event, then state machine should go to state OnGoingLoginState.

Starting custom BaseStateableHandler

To make LoginStateableHandler work, you must remember to call it's onCreate(Bundle savedInstanceState), onResume(), onPause(), onSaveInstanceState(Bundle outState) methods in appropriate Fragment/Activity lifecycle method's. Sample usage:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    ...
    handler = new LoginStateableHandler();
    handler.onCreate(savedInstanceState);
}

@Override
protected void onResume() {
    super.onResume();
    handler.onResume();
}

@Override
protected void onPause() {
    super.onPause();
    handler.onPause();
}

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    handler.onSaveInstanceState(outState);
}

Of course you can initialize handler from other places, not only Fragment/Activity. Here is an example of starting handler in singleton class like Application:

public class MyApplication extends Application {

    LoginStateableHandler handler;

    @Override
    public void onCreate() {
        super.onCreate();

        handler = new LoginStateableHandler();
        handler.onCreate(null);
        handler.onResume();
    }
}

Creating states

State machine consist of states. Each state should extends State that contains two methods:

• onStateApplied() - called when entering state
• onStateLeft() - called when leaving state

Each state should call fireEvent(int eventId) when it finish it's job. Sample State:

public class OnGoingLoginState extends State<LoginProvider, LoginActionInterface>{

    @Inject
    Bus bus;

    @Inject
    NetworkManager networkManager;

    public OnGoingLoginState() {
        Application.getComponentInstance().inject(this);
    }

    @Override
    public void onStateApplied() {
        bus.register(this);
    }

    @Override
    public void onStateLeft() {
        bus.unregister(this);
    }

    @Subscribe
    public void onBusLoginEvent(BusLoginEvent loginEvent) {
        networkManager.loginUser(loginEvent.getEmail(), loginEvent.getPassword());
        fireEvent(LoginEvents.SENDING_IN_PROGRESS);
    }
}

It is nice to use some Bus implementation, like EventBus or Otto, to receive applications events.

Used libraries

• [otto] https://github.com/square/otto
• [dagger 2] https://github.com/google/dagger
• [spock] https://code.google.com/p/spock/
• [android support library v7]

LICENSE

LICENSE