关于PinnedHeaderExpandableListView使用的时候on a null object reference

天天在各种博客论坛学习大神们的代码，所以觉得也应该把自己的东西拿出来分享和提问，如果有用不用谢我，如果无用也不要骂我，谢谢各位

问题：今天要写一个分组的ListView带分组悬停效果的，看到这篇博文http://blog.csdn.net/h7870181/article/details/40400155，就直接用了。但是博主数据源用的是二维数组存放的，所以自己用List<List<Object>>的方式存放，结果使用的时候直接崩溃了，跟着log找到问题的地方

@Override

protected
void onLayout(boolean changed,
int left, int top,
int right,

int bottom) {

super.onLayout(changed, left, top, right, bottom);

final
long flatPostion = getExpandableListPosition(getFirstVisiblePosition());

final
int groupPos = ExpandableListView

.getPackedPositionGroup(flatPostion);

final
int childPos = ExpandableListView

.getPackedPositionChild(flatPostion);

int state = mAdapter.getHeaderState(groupPos, childPos); 这里报错 on a null object reference 大概是说引用了空的对象吧

if (mHeaderView !=
null && null != mAdapter
&& state != mOldState) {

mOldState = state;

mHeaderView.layout(0, 0,
mHeaderViewWidth, mHeaderViewHeight);

}

configureHeaderView(groupPos, childPos);

}

找不到问题出在哪里，不过后来把这里改成这样就可以，但是为什么会空值就不清楚了，知道的请留言说说，谢谢

@Override

protected
void onLayout(boolean changed,
int left, int top,
int right,

int bottom) {

super.onLayout(changed, left, top, right, bottom);

final
long flatPostion = getExpandableListPosition(getFirstVisiblePosition());

final
int groupPos = ExpandableListView

.getPackedPositionGroup(flatPostion);

final
int childPos = ExpandableListView

.getPackedPositionChild(flatPostion);

if (null !=
mAdapter) {

int state =
mAdapter.getHeaderState(groupPos, childPos);

if (mHeaderView !=
null && state != mOldState) {

mOldState = state;

mHeaderView.layout(0, 0,
mHeaderViewWidth, mHeaderViewHeight);

}

}

configureHeaderView(groupPos, childPos);

}