借助于android中的加速度计和加速中的平滑移动球

Question

import android.app.Activity;
import android.content.Context;
import android.content.pm.ActivityInfo;
import android.content.res.Configuration;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.drawable.ShapeDrawable;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.view.Display;
import android.view.View;
import android.view.Window;
import android.view.WindowManager;

public class MainActivity extends Activity implements SensorEventListener {

    CustomDrawableView mCustomDrawableView = null;
    ShapeDrawable mDrawable = new ShapeDrawable();
    public float xPosition, xAcceleration, xVelocity = 0.0f;
    public float yPosition, yAcceleration, yVelocity = 0.0f;
    public float xmax, ymax;
    private Bitmap mBitmap;
    private Bitmap mWood;
    private SensorManager sensorManager = null;
    public float frameTime = 0.666f;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        // Set FullScreen & portrait
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
                WindowManager.LayoutParams.FLAG_FULLSCREEN);
        setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);

        // Get a reference to a SensorManager
        sensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
        sensorManager.registerListener(this,
                sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER),
                SensorManager.SENSOR_DELAY_GAME);

        mCustomDrawableView = new CustomDrawableView(this);
        setContentView(mCustomDrawableView);
        // setContentView(R.layout.main);

        // Calculate Boundry
        Display display = getWindowManager().getDefaultDisplay();
        xmax = (float) display.getWidth() - 50;
        ymax = (float) display.getHeight() - 50;
    }

    // This method will update the UI on new sensor events
    public void onSensorChanged(SensorEvent sensorEvent) {
        {
            if (sensorEvent.sensor.getType() == Sensor.TYPE_ORIENTATION) {
                // Set sensor values as acceleration
                yAcceleration = sensorEvent.values[1];
                xAcceleration = sensorEvent.values[2];
                updateBall();
            }
        }
    }

    private void updateBall() {

        // Calculate new speed
        xVelocity += (xAcceleration * frameTime);
        yVelocity += (yAcceleration * frameTime);

        // Calc distance travelled in that time
        float xS = (xVelocity / 2) * frameTime;
        float yS = (yVelocity / 2) * frameTime;

        // Add to position negative due to sensor
        // readings being opposite to what we want!
        xPosition -= xS;
        yPosition -= yS;

        if (xPosition > xmax) {
            xPosition = xmax;
        } else if (xPosition < 0) {
            xPosition = 0;
        }
        if (yPosition > ymax) {
            yPosition = ymax;
        } else if (yPosition < 0) {
            yPosition = 0;
        }
    }

    // I've chosen to not implement this method
    public void onAccuracyChanged(Sensor arg0, int arg1) {
        // TODO Auto-generated method stub
    }

    @Override
    protected void onResume() {
        super.onResume();
        sensorManager.registerListener(this,
                sensorManager.getDefaultSensor(Sensor.TYPE_ORIENTATION),
                SensorManager.SENSOR_DELAY_GAME);
    }

    @Override
    protected void onStop() {
        // Unregister the listener
        sensorManager.unregisterListener(this);
        super.onStop();
    }

    public class CustomDrawableView extends View {
        public CustomDrawableView(Context context) {
            super(context);
            Bitmap ball = BitmapFactory.decodeResource(getResources(),
                    R.drawable.ball);
            final int dstWidth = 50;
            final int dstHeight = 50;
            mBitmap = Bitmap
                    .createScaledBitmap(ball, dstWidth, dstHeight, true);
        }

        protected void onDraw(Canvas canvas) {
            final Bitmap bitmap = mBitmap;
            canvas.drawBitmap(bitmap, xPosition, yPosition, null);
            invalidate();
        }
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        // TODO Auto-generated method stub
        super.onConfigurationChanged(newConfig);
        setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
    }
}

球似乎被冻结而没有移动它没有检测到的动作。 移动设备时，球的加速度也应平稳。 请帮我解释这段代码，尽量解释，因为我是android的新手。

提前谢谢。