android - 如何将箭头指向特定方向，即西

Question

无论用户面向何处，我都想将我的箭头视图仅指向西方向。下面是我尝试过但没有得到预期结果的代码。

// inside onCreate()
sensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
    gsensor = sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
    msensor = sensorManager.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);
    packageManager = getPackageManager();
    if (packageManager.hasSystemFeature(PackageManager.FEATURE_SENSOR_COMPASS)){
        sensorManager.registerListener(this, gsensor, SensorManager.SENSOR_DELAY_GAME);
        sensorManager.registerListener(this, msensor, SensorManager.SENSOR_DELAY_GAME);
    }else {
        Toast.makeText(MainActivity.this,"No Compass Sensor !", Toast.LENGTH_SHORT).show();
    }


 @Override
public void onSensorChanged(SensorEvent event) {

    final float alpha = 0.97f;

    synchronized (this){
        if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER){
            mGravity[0] = alpha * mGravity[0] + (1 - alpha)
                    * event.values[0];
            mGravity[1] = alpha * mGravity[1] + (1 - alpha)
                    * event.values[1];
            mGravity[2] = alpha * mGravity[2] + (1 - alpha)
                    * event.values[2];
        }

        if (event.sensor.getType() == Sensor.TYPE_MAGNETIC_FIELD){
            mGeomagnetic[0] = alpha * mGeomagnetic[0] + (1 - alpha)
                    * event.values[0];
            mGeomagnetic[1] = alpha * mGeomagnetic[1] + (1 - alpha)
                    * event.values[1];
            mGeomagnetic[2] = alpha * mGeomagnetic[2] + (1 - alpha)
                    * event.values[2];
        }

        float R[] = new float[9];
        float I[] = new float[9];
        boolean success = SensorManager.getRotationMatrix(R, I, mGravity, mGeomagnetic);
        if (success){
            float orientation[] = new float[3];
            SensorManager.getOrientation(R, orientation);
            azimuth = (float) Math.toDegrees(orientation[0]);
            Log.i("DegreeA",""+azimuth);
            azimuth = (azimuth + 360) % 270;
            Log.i("DegreeA",""+azimuth);
            adjustThearrow();
        }
    }
}

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

}

private void adjustThearrow(){


    Matrix matrix = new Matrix();
    imageview.setScaleType(ImageView.ScaleType.MATRIX);   
    matrix.postRotate((float) -azimuth, imageview.getDrawable().getBounds().width()/2,
            imageview.getDrawable().getBounds().height()/2);

    imageview.setImageMatrix(matrix);
}

在下面的代码行中，如果我设置 360 而不是 270，它会给我一个仅指向北方向的箭头，并且它会平滑旋转。

azimuth = (azimuth + 360) % 360;

但是如果我想让我的代码只面向西方向的箭头，我已经设置了这样的代码：

azimuth = (azimuth + 360) % 270;

但这一次旋转并不顺畅。

请帮助我如何进行。如果提供任何替代解决方案会更好。

标签： androidmathsensorscompasscompass-geolocation