未使用的字段的值

Question

我在我的Android应用程序中遇到此问题，因为“该字段的值未被使用”。 实际上我正在尝试播放用户滑动页面时的声音，但它不断给我这个错误。这是我的代码。

包com.android.learning_numbers;

import android.media.MediaPlayer;
import android.os.Bundle;
import android.app.Activity;
import android.content.Context;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v4.view.ViewPager.OnPageChangeListener;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;

public class Numbers extends Activity {

    private static final OnPageChangeListener mOnPageListener = null;
    public static MediaPlayer mp = null;

    @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_numbers);
         ViewPager viewPager = (ViewPager)findViewById(R.id.view_pager);
         ImagePagerAdapter adapter = new ImagePagerAdapter();
         viewPager.setAdapter(adapter);
         viewPager.setOnPageChangeListener(mOnPageListener);

     }

     private class ImagePagerAdapter extends PagerAdapter {

         private int[] mImages = new int[] {R.drawable.no1,R.drawable.no2,R.drawable.no3,R.drawable.no4,R.drawable.no5,R.drawable.no6,R.drawable.no7,R.drawable.no8,R.drawable.no9,};


         private int[] mAudio= new int[]{R.raw.one,R.raw.two,R.raw.three,R.raw.four,R.raw.five,R.raw.six,R.raw.seven,R.raw.eight,R.raw.nine,};
         @Override
         public int getCount() {
         return mImages.length;
           }
         @Override
         public boolean isViewFromObject(View view, Object object) {
            return view == ((ImageView) object);
               }
         @Override
         public Object instantiateItem(ViewGroup container, int position) {
            Context context = Numbers.this;
            ImageView imageView = new ImageView(context);
            int padding =context.getResources().  
            getDimensionPixelSize(R.dimen.activity_vertical_margin);
            imageView.setPadding(padding, padding, padding, padding);
            imageView.setScaleType(ImageView.ScaleType.CENTER);
            imageView.setImageResource(mImages[position]);
            ((ViewPager) container).addView(imageView, 0); 
            return imageView;
            }

         public OnPageChangeListener mOnPageListener = new OnPageChangeListener() {

             @Override public void onPageSelected(int position) {
                 //for Sound 
                 if (mp != null) {
                     mp.reset();
                     mp.release();
                 }
                 mp = MediaPlayer.create(Numbers.this, mAudio[position]);
                 mp.start();
             }
             @Override public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {}
             @Override public void onPageScrollStateChanged(int state) {}

         };



         @Override
         public void destroyItem(ViewGroup container, int position, Object object) {
           ((ViewPager) container).removeView((ImageView) object);
         }
     }
     }