获取nullpointer异常viewPager.getChildAt（viewPager.getCurrentItem（））;安卓

Question

每当我尝试viewPager.getChildAt时，我都会收到空指针异常 我附上了代码snippshot

// Scroll Page Limit
private int scrollPageLimit = Integer.MAX_VALUE / 2;
private int lastPageSelected = scrollPageLimit;

viewPager = (ViewPager) findViewById(R.id.calendar);

    MyPagerAdapter adapter = new MyPagerAdapter(context);
    //PagerAdapter wrappedAdapter = new InfinitePagerAdapter(adapter);
    viewPager.setAdapter(adapter);
    viewPager.setCurrentItem(scrollPageLimit);
    LinearLayout view = (LinearLayout) viewPager.getChildAt(viewPager.getCurrentItem());
    GridView calendar = (GridView) view.findViewById(R.id.gridView_calendar);


// My Adapter
private class MyPagerAdapter extends PagerAdapter {

    // int NumberOfPages = scrollPageLimit*2 + 1;
    Context context;

    public MyPagerAdapter(Context context) {
        this.context = context;
    }

    @Override
    public int getCount() {
        return Integer.MAX_VALUE;
    }

    @Override
    public boolean isViewFromObject(View view, Object object) {
        return view == object;
    }

    @Override
    public Object instantiateItem(ViewGroup container, int position) {

        Log.v("ExtendedCalendarView", "instantiateItem : "+position );
        LayoutInflater inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        LinearLayout view = (LinearLayout) inflater.inflate(
                R.layout.viewpager_calendar, null);
        GridView calendar = (GridView) view
                .findViewById(R.id.gridView_calendar);
        <!-- Calendar generation code -->
        view.setTag(new MonthYearTagPager(cal.get(Calendar.MONTH), cal.get(Calendar.YEAR)));
        return view;

    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        Log.v("ExtendedCalendarView", "destroyItem : "+position );

        container.removeView((LinearLayout) object);
    }


}

<!--layout  viewpager_calendar -->

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/linear"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#F1F0EB"
android:orientation="vertical" >

<TextView
    android:id="@+id/textView_month"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center_horizontal"
    android:text="TextView"
    android:textAppearance="?android:attr/textAppearanceSmallInverse" />

   <GridView
     android:id="@+id/gridView_calendar"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:background="#fff"
        android:listSelector="@android:color/transparent"
        android:numColumns="7">
</GridView>

如果我将访问LinearLayout view =（LinearLayout）viewPager.getFocusedChild（）;然后它工作，但它返回下一个viewpager元素。