Adding a sensor to the Android App

This Tutorial will explain how the Cosmic (CO__mputer __S__cientists __M__aking mus__IC) Android App can be extended. We will implement a proximity sensor. In most Android devices the built-in proximity sensor returns just two different values, which indicate if an object (usually the head of the user) is near or far. The values from the sensor will be mapped to a certain range, which is provided by the Synthesizer. The mapped value is then send via an OSC message to the Synthesizer.

Contents
1. Sensor listener for an Android sensor
2. Custom row layout
3. Layout inflater and controller
4. Registration of the sensor

Sensor listener for an Android sensor

First of all we will create a listener class that receives updates from the sensor via a callback method onSensorChanged. The constructor of the class calls the constructor of the superclass AbstractSensorListener to register the listener. The onSensorChanged method notifys observers (see below) once the value of the sensor changes. The getters grant the observers access to this data.

public class ProximitySensorListener extends AbstractSensorListener {
    private float value;

    public ProximitySensorListener(Context context) {
        super(context, Sensor.TYPE_PROXIMITY);

        value = 0;
    }

    @Override
    public void onSensorChanged(SensorEvent event) {
        if(event.sensor.getType() != getSensorType())
            return;

        float current_value = event.values[0];
        if(current_value != value) {
            value = current_value;

            setChanged();
            notifyObservers();
        }
    }

    public float getProximityValueInPercent() {
        return value / getSensorManager().getDefaultSensor(getSensorType()).getMaximumRange();
    }

    public float getProximityValue() {
        return value;
    }
}

Custom row layout

Each sensor has a custom UI layout. The layout is loaded as one row in the ListView of the interaction fragment. In this case we make a simple layout that displays the OSC message (@+id/msg) above the descriptive text “Proximity:” which is right next to the current proximity value (@+id/value). The next section explains how the layout is filled with data.

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/msg" />

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="fill_parent">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Proximity:"
            android:paddingRight="10dp" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/value" />
    </LinearLayout>

</LinearLayout>

Layout inflater and controller

The following class implements the InteractionRow interface which extends Javas Observer interface and declares two new functions getView and getViewType. getView uses the View Holder-Pattern and instanciates the layout. The getViewType function distinguishes between the different row types (sensors, see below). The constructor instanciates the listener and adds itself as a listener. The update function is called once the values of the sensor change. It updates the OSC message (the model) and sends the message to the Synthesizer. It also triggers the UI update.

public class InteractionProximityRow implements InteractionRow {
    private final OSCMessage msg;
    private final LayoutInflater inflater;
    private final ProximitySensorListener listener;

    private ViewHolder holder;

    @Override
    public void update(Observable observable, Object o) {
        final float p = listener.getProximityValueInPercent();
        msg.setValueAsPercent(p);
        OSCSender.send(msg);

        updateUI();
    }

    private void updateUI() {
        if(holder != null) {
            // Using AsyncTask.onPostExecute to update UI (UI-Updates must happen on UI thread)
            new AsyncTask<Void, Void, Void>() {
                @Override
                protected Void doInBackground(Void... voids) {
                    return null;
                }
                @Override
                protected void onPostExecute(Void result) {
                    holder.value.setText(listener.getProximityValue() + " cm");
                }
            }.execute();
        }
    }

    private static class ViewHolder {
        final TextView msgText;
        final TextView value;

        private ViewHolder(TextView msgText, TextView value) {
            this.msgText = msgText;
            this.value = value;
        }
    }


    public InteractionProximityRow(LayoutInflater inflater, OSCMessage msg) {
        this.inflater = inflater;
        this.msg = msg;
        this.holder = null;

        this.listener = new ProximitySensorListener(inflater.getContext());
        this.listener.addObserver(this);
    }


    @Override
    public View getView(View convertView) {
        View view;

        // no convertView so create a new one
        if (convertView == null) {
            ViewGroup viewGroup = (ViewGroup) inflater.inflate(R.layout.interaction_row_proximity, null);

            holder = new ViewHolder(
                    (TextView) viewGroup.findViewById(R.id.msg),
                    (TextView) viewGroup.findViewById(R.id.value)
            );

            viewGroup.setTag(holder);

            view = viewGroup;
        } else {
            holder = (ViewHolder) convertView.getTag();

            view = convertView;
        }

        // actually setup the view
        holder.msgText.setText(msg.getPath());

        return view;
    }

    @Override
    public int getViewType() {
        return InteractionMethod.PROXIMITY.ordinal();
    }
}

Registration of the sensor

Finally all sensors are enumerated in the InteractionMethod enum. The layout inflater class must be specified (please make sure its constructor takes a LayoutInflater and an OSCMessage as parameters) to correctly load all classes. The second parameter is the description by which the users chooses the sensor.

public enum InteractionMethod {
    SEEKBAR(InteractionSeekBarRow.class, "Slider"),
    BUTTON(InteractionButtonRow.class, "Button"),
    TILT(InteractionTiltRow.class, "Tilt"),
    ROTARYZ(InteractionRotaryZRow.class, "Rotary Switch"),
    SHAKE(InteractionShakeRow.class, "Shake"),
    LIGHT(InteractionLightRow.class, "Light"),
    PROXIMITY(InteractionProximityRow.class, "Proximity");

    ...