在viewpager中滑动时，getActivity（）总是返回null？

Question

我正在使用fragmentstatepageadapter来实现viewpage。 我已经动态添加了片段但是当我在页面上滑动时，getActivity（）会抛出NPE。 我也提到大多数解决方案都没有工作。

这是我的pagechange监听器

viewPager.setOnPageChangeListener(new OnPageChangeListener() {

private     int scrollState=-1;
private     int oldFrag=-1;
private     int newFrag=-1;

@Override
public void onPageSelected(int newPositon) {

    Log.d("LMTLOGGERR", "get current page selected :: "+newPositon);
    currentTabItem=newPositon;

    Fragment new_fragment = mPageStateAdapter.getItem(newPositon);
    new_fragment.setUserVisibleHint(true);
    new_fragment.onResume();
    if(oldFrag>=0){
        Fragment ol_fragment= mPageStateAdapter.getItem(oldFrag);
        ol_fragment.setUserVisibleHint(false);
        ol_fragment.onPause();
    }   

    newFrag=newPositon;
    oldFrag=newFrag;
}

@Override 
public void onPageScrolled(int position , float positionOffset, int positionOffsetPixel) {

    if(positionOffset==0.0 &&  position+1==TabList.size() &&
                    scrollState==ViewPager.SCROLL_STATE_DRAGGING)
            {
                //viewPager.setCurrentItem(0);
            }


}

@Override
public void onPageScrollStateChanged(int state) {
    scrollState=state;
    Log.d("LMTLOGGERR", "SCROLL_STATE_DRAGGING"+ViewPager.SCROLL_STATE_DRAGGING+"SCROLL_STATE_IDLE"+ViewPager.SCROLL_STATE_IDLE+
                        "SCROLL_STATE_SETTLING"+ViewPager.SCROLL_STATE_SETTLING+"current state"+state);

    }
});

我的页面适配器

class PageStateAdapter extends FragmentStatePagerAdapter{
public PageStateAdapter(FragmentManager fm){
    super(fm);
}

@Override
public Fragment getItem(int arg0) {

    if(TabList.get(arg0).equalsIgnoreCase("profile")){
        Fragment fragment = new VTMTMyProf();
        return fragment;
    }else if(TabList.get(arg0).equalsIgnoreCase("Video")){
       // args.putInt(DemoObjectFragment.ARG_OBJECT, i + 1); // Our object is just an integer :-P
       Fragment fragment = new VTMTVideoActivity();
       Bundle args = new Bundle();
        Object obj = productsListData;
     args.putSerializable("product",(Serializable) obj);

     args.putString("check", "fragment");
        fragment.setArguments(args);
        return fragment;
    }else if(TabList.get(arg0).equalsIgnoreCase("Document")){
        Fragment fragment = new  VTMTDocList();
        Bundle args = new Bundle();
       // args.putInt(DemoObjectFragment.ARG_OBJECT, i + 1); // Our object is just an integer :-P

    Object obj = productsListData;
     args.putSerializable("product",(Serializable) obj);

     args.putString("check", "fragment");
        fragment.setArguments(args);
        return fragment;

    }else if(TabList.get(arg0).equalsIgnoreCase("Sales Tip")){
        Fragment fragment = new VTMTSalesTip();
        Bundle args = new Bundle();
           // args.putInt(DemoObjectFragment.ARG_OBJECT, i + 1); // Our object is just an integer :-P

            Object obj = productsListData;
         args.putSerializable("product",(Serializable) obj);

         args.putString("check", "fragment");
            fragment.setArguments(args);
            return fragment;
    }else if(TabList.get(arg0).equalsIgnoreCase("Quiz")){
        Fragment fragment = new VTMTQuizList();
        Bundle args = new Bundle();
           // args.putInt(DemoObjectFragment.ARG_OBJECT, i + 1); // Our object is just an integer :-P

            Object obj = productsListData;
         args.putSerializable("product",(Serializable) obj);

         args.putString("check", "fragment");
            fragment.setArguments(args);
            return fragment;
    }else{
        //analytics
        Fragment fragment = new VTMTNewAnalytics();
         Bundle args = new Bundle();
           // args.putInt(DemoObjectFragment.ARG_OBJECT, i + 1); // Our object is just an integer :-P
            Object obj = productsListData;
         args.putSerializable("product",(Serializable) obj);

         args.putString("check", "fragment");
            fragment.setArguments(args);
            return fragment;
    }

我在这个片段类中获得了NPE

((Activity)mContext).runOnUiThread(new Runnable() {
    public void run() {
        listAdapter.notifyDataSetChanged();
    }
});

我在onActtach（Activity）中初始化了mContext