Zero division exception is thrown when viewpager and adapter are created, and there is no data in adapter (it appears later, e.g. loaded from internet). Viewpager adapter's wrapper tries to determine realPosition but fails. Also added gradle support

Hi,

I'm wondering if there is a special way to notify the adapter with this lib ? The readme specifie two adapter, can we get access to the second one ?

Make wrapping adapter empty when the wrapped adapter is empty. Before when the wrapped adapter returned 0 from getCount(), signaling that it doesn't want to create any pages, the wrapping adapter returned 2. Because of that view pager could still call instantiateItem(). In my case my wrapped adapter wasn't ready at all to run instantiateItem() while getCount() returned 0 and it crashed. Thanks to this change view pager is blank until I add some data, which is exactly what I expect.

Fragment with a FragmentPagerAdapter will now have setUserVisibleHint called when shown.

Based on this StackOverflowQuestion: http://stackoverflow.com/questions/10024739/how-to-determine-when-fragment-becomes-visible-in-viewpager

The PagerAdapter should forward and delegate the setPrimaryItem to allow for FragmentPagerAdapter to call the setUserVisibleHint methods to true.

When use it my app do crash: Here is my code :

tablayout.setupWithViewPager(mLoopingViewPager);

Here is my logcat:

App has crashed, executing CustomActivityOnCrash's UncaughtExceptionHandler java.lang.IndexOutOfBoundsException: Invalid index 4, size is 1 at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:255) at java.util.ArrayList.get(ArrayList.java:308) at android.support.design.widget.TabLayout.getTabAt(TabLayout.java:518) at android.support.design.widget.TabLayout$TabLayoutOnPageChangeListener.onPageSelected(TabLayout.java:1986) at android.support.v4.view.ViewPager.dispatchOnPageSelected(ViewPager.java:1867) at android.support.v4.view.ViewPager.scrollToItem(ViewPager.java:629) at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:609) at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:570) at android.support.v4.view.ViewPager.setCurrentItem(ViewPager.java:562) at com.imbryk.viewPager.LoopViewPager.setCurrentItem(LoopViewPager.java:110)

When I use addOnPageChangeListener instead setOnPageChangeListener, it will lead to some unpredictable problems. Add the following code to fix it in LoopViewPager:: 【当我使用addOnPageChangeListener代替setOnPageChangeListener，这将导致一些不可预知的问题。在LoopViewPager中添加以下代码作简单的修复：】

    @Deprecated
    @Override
    public void addOnPageChangeListener(OnPageChangeListener listener) {
        // only support one listener, use setOnPageChangeListener instead
        mOuterPageChangeListener = listener;
    }

public class SimpleGalleryAdapter extends PagerAdapter {

private List<T> mDatas;
private String imgFieldName;
private SparseArray<ImageView> mCaches = new SparseArray<>();
private String host;
private OnImageLoadListener<T> mListener;

@Override
public int getCount() {
    return EmptyUtils.emptyOfList(mDatas) ? 0 : mDatas.size();
}

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

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

    Context context = container.getContext();
    ImageView img_display = mCaches.get(position);

    if (img_display == null) {
        img_display = new ImageView(context);
        img_display.setScaleType(ImageView.ScaleType.CENTER_CROP);
        mCaches.put(position, img_display);
    }

    T mItem = mDatas.get(position);

    if (mListener != null) {
         mListener.onImageLoad(img_display, mItem, imgFieldName, host);
    }
    container.addView(img_display);
    return img_display;
}

@Override
public void destroyItem(ViewGroup container, int position, Object object) {
    if (mCaches.keyAt(position) != -1) {
        container.removeView(mCaches.get(position));
        mCaches.remove(position);
    }
}

public SimpleGalleryAdapter(List<T> mDatas, String host, String imgFieldName, OnImageLoadListener<T> mListener) {
    this.mDatas = mDatas;
    this.imgFieldName = imgFieldName;
    this.host = host;
    this.mListener = mListener;
}

public SimpleGalleryAdapter(List<T> mDatas, String host, String imgFieldName) {
    this.mDatas = mDatas;
    this.imgFieldName = imgFieldName;
    this.host = host;
    this.mListener = new GlideImageLoader<T>();
}

}

that is my adapter , I user ViewPager no error , but use LoopViewPager throw this error The specified child already has a parent. You must call removeView() on the child's parent first.

The application's PagerAdapter changed the adapter's contents without calling PagerAdapter#notifyDataSetChanged! Expected adapter item count: 6, found: 2