关于在内部类中启动一个Android Intent的疑惑

在网上看到的所有android例子都是把adapter和listener写在一起，多是内部类的实现方式。我今天想把他们分离开。即adapter和listener写在一个class里面，adapter和listener在同一个class中以内部类形式存在。但是adapter在相关操作上正常，但是listener缺出现启动一个activity时null指针问题。代码如下

在一个JshopActivityIndex中我使用了viewpager控件

我先把viewpager的相关adapter和listener写在了JshopViewpagerAdapter

package com.jshop.android.widget;import java.util.ArrayList;import com.jshop.android.index.JshopActivityIndex;import com.jshop.android.index.JshopMIndex;import com.jshop.android.index.R;import com.jshop.android.index.WelcomeAct;import android.app.Activity;import android.content.Context;import android.content.Intent;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.widget.ImageView;public class JshopViewpagerAdapter extends Activity {public class JshopActivityIndexViewpagerAdapter extends PagerAdapter {private ArrayList<View> pageViews;public JshopActivityIndexViewpagerAdapter() {super();// TODO Auto-generated constructor stub}/** * 对左右滚动空间进行适配器定义和操作 */public JshopActivityIndexViewpagerAdapter(ArrayList<View> pv) {this.pageViews = pv;}@Overridepublic int getCount() {return pageViews.size();}@Overridepublic boolean isViewFromObject(View arg0, Object arg1) {return arg0 == arg1;}@Overridepublic void destroyItem(View container, int position, Object object) {((ViewPager) container).removeView(pageViews.get(position));}@Overridepublic void finishUpdate(View container) {// TODO Auto-generated method stub}@Overridepublic Object instantiateItem(View container, int position) {// TODO Auto-generated method stub((ViewPager) container).addView(pageViews.get(position));return pageViews.get(position);}@Overridepublic void setPrimaryItem(View container, int position, Object object) {// TODO Auto-generated method stubsuper.setPrimaryItem(container, position, object);}@Overridepublic void startUpdate(View container) {// TODO Auto-generated method stubsuper.startUpdate(container);}} // 指引页面更改事件监听器    public class JshopActivityIndexViewpagerPageChangeListener  implements OnPageChangeListener {      private Context context;    private ImageView[] imageViews;        public JshopActivityIndexViewpagerPageChangeListener(Context ctx,ImageView[] v){    this.context=ctx;    this.imageViews=v;    }        @Override          public void onPageScrollStateChanged(int arg0) {              // TODO Auto-generated method stub          }          @Override          public void onPageScrolled(int arg0, float arg1, int arg2) {              // TODO Auto-generated method stub          }            @Override          public void onPageSelected(int arg0) {            for (int i = 0; i < imageViews.length; i++) {                  imageViews[arg0].setBackgroundResource(R.drawable.page_indicator_focused);                                if (arg0 != i) {                      imageViews[i].setBackgroundResource(R.drawable.page_indicator);                  }              }            if(arg0==5){            Intent intent = new Intent(context,JshopMIndex.class);startActivity(intent);            }        }      }}

当程序执行到

 if(arg0==5){            Intent intent = new Intent(context,JshopMIndex.class);startActivity(intent);            }

启动另一个activity时候就会报错。

我是这样调用这个内部类的

viewPager.setAdapter(new JshopViewpagerAdapter().new JshopActivityIndexViewpagerAdapter(pageViews));viewPager.setOnPageChangeListener(new JshopViewpagerAdapter().new JshopActivityIndexViewpagerPageChangeListener(JshopActivityIndex.this,imageViews));

我也在网上查到了类似问题地址是

http://stackoverflow.com/questions/6140157/startactivityforresult-null-pointer-exception-context

我心里想把adapter和listener分离，可以让activity的代码不用那么长，可是目前只能做到分离adapter。希望有高人指点下