RNSimpleCompassModule.java

package com.reactlibrary;

import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;

import android.content.Context;

import com.facebook.react.bridge.WritableMap;
import com.facebook.react.modules.core.DeviceEventManagerModule;
import com.facebook.react.bridge.Arguments;

import com.facebook.react.bridge.ReactApplicationContext;
import com.facebook.react.bridge.ReactContextBaseJavaModule;
import com.facebook.react.bridge.ReactMethod;
import com.facebook.react.bridge.Callback;

public class RNSimpleCompassModule extends ReactContextBaseJavaModule implements SensorEventListener {

  private final ReactApplicationContext reactContext;

  private static Context mApplicationContext;
  private int mAzimuth = 0; // degree
  private int mFilter = 1;
  private SensorManager mSensorManager;
  private Sensor mSensor;
  private float[] orientation = new float[3];
  private float[] rMat = new float[9];

  public RNSimpleCompassModule(ReactApplicationContext reactContext) {
    super(reactContext);
    this.reactContext = reactContext;
    mApplicationContext = reactContext.getApplicationContext();
  }

  @Override
  public String getName() {
    return "RNSimpleCompass";
  }

  @ReactMethod
  public void start(int filter) {

      if (mSensorManager == null) {
          mSensorManager = (SensorManager) mApplicationContext.getSystemService(Context.SENSOR_SERVICE);
      }

      if (mSensor == null) {
          mSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_ROTATION_VECTOR);
      }

      mFilter = filter;
      mSensorManager.registerListener(this, mSensor, SensorManager.SENSOR_DELAY_UI);
  }

  @ReactMethod
  public void stop() {
    if (mSensorManager != null) {
      mSensorManager.unregisterListener(this);
    }
  }

  @Override
  public void onSensorChanged(SensorEvent event) {
      if( event.sensor.getType() == Sensor.TYPE_ROTATION_VECTOR ){
          // calculate th rotation matrix
          SensorManager.getRotationMatrixFromVector(rMat, event.values);
          // get the azimuth value (orientation[0]) in degree
          int newAzimuth = (int) ( Math.toDegrees( SensorManager.getOrientation( rMat, orientation )[0] ) + 360 ) % 360;

          //dont react to changes smaller than the filter value
          if (Math.abs(mAzimuth - newAzimuth) < mFilter) {
              return;
          }

          mAzimuth = newAzimuth;
          WritableMap map = Arguments.createMap();

          map.putDouble("heading", mAzimuth);
          map.putDouble("accuracy",event.accuracy);

          getReactApplicationContext()
                  .getJSModule(DeviceEventManagerModule.RCTDeviceEventEmitter.class)
                  .emit("HeadingUpdated", map);
      }
  }


  @Override
  public void onAccuracyChanged(Sensor sensor, int accuracy) {

  }
}