Android开发中遇到的一个问题 明明存在该类却报错classnotfound

如题，下面贴报错地方的代码

 
public void setAdapter(PagerAdapter adapter) {
        if (mAdapter != null) {
            VerticalViewPagerCompat.setDataSetObserver(mAdapter, null);
        }
 
        mAdapter = adapter;
 
        if (mAdapter != null) {
            if (mObserver == null) {
                mObserver = new DataSetObserver();
            }
            VerticalViewPagerCompat.setDataSetObserver(mAdapter, mObserver);
            mPopulatePending = false;
            if (mRestoredCurItem >= 0) {
                mAdapter.restoreState(mRestoredAdapterState,
                        mRestoredClassLoader);
                setCurrentItemInternal(mRestoredCurItem, false, true);
                mRestoredCurItem = -1;
                mRestoredAdapterState = null;
                mRestoredClassLoader = null;
            } else {
                populate();
            }
        }
    }

当中

`

mObserver = new DataSetObserver();
`

会提示 ClassNotFound，找不到这个DataSetObserver类，但是我在同一个文件中，自己新建了个这个类，代码如下

 
private class DataSetObserver implements
            VerticalViewPagerCompat.DataSetObserver {
        @Override
        public void onDataSetChanged() {
            dataSetChanged();
        }
    }