listView疑难杂症专科，没感冒也来看看。

Question

代码向上

 private List<String> mList;
 private SimpleAdapter mAdapter;
 private ListView mLv;
 public void onCreate(Bundle saveIn){
     mLv = (ListView)findViewByID(R.id.lv);
     mList = new ArrayList();
     mList.add("123");
     mLv.setAdapter(mAdapter);
     mAdapter = new SimpleAdapter(this,mList,android.R.layout.item_1_simple);
 }

看出问题了吗？
上面执行setAdapter的时候mAdapter其实还没初始化，但不会报错。不过数据不会显示出来。
setAdapter（）方法源码：

  @Override
    public void setAdapter(ListAdapter adapter) {
        if (mAdapter != null && mDataSetObserver != null) {
            mAdapter.unregisterDataSetObserver(mDataSetObserver);
        }

        resetList();
        mRecycler.clear();

        if (mHeaderViewInfos.size() > 0|| mFooterViewInfos.size() > 0) {
            mAdapter = new HeaderViewListAdapter(mHeaderViewInfos, mFooterViewInfos, adapter);
        } else {
            **mAdapter = adapter;**
        }

        mOldSelectedPosition = INVALID_POSITION;
        mOldSelectedRowId = INVALID_ROW_ID;

        // AbsListView#setAdapter will update choice mode states.
        super.setAdapter(adapter);

        if (mAdapter != null) {
            mAreAllItemsSelectable = mAdapter.areAllItemsEnabled();
            mOldItemCount = mItemCount;
            mItemCount = mAdapter.getCount();
            checkFocus();

            mDataSetObserver = new AdapterDataSetObserver();
            mAdapter.registerDataSetObserver(mDataSetObserver);

            mRecycler.setViewTypeCount(mAdapter.getViewTypeCount());

            int position;
            if (mStackFromBottom) {
                position = lookForSelectablePosition(mItemCount - 1, false);
            } else {
                position = lookForSelectablePosition(0, true);
            }
            setSelectedPositionInt(position);
            setNextSelectedPositionInt(position);

            if (mItemCount == 0) {
                // Nothing selected
                checkSelectionChanged();
            }
        } else {
            mAreAllItemsSelectable = true;
            checkFocus();
            // Nothing selected
            checkSelectionChanged();
        }

        requestLayout();
    }

关键应该是加粗代码没执行，本人觉得问题就在这里了。
但是：

  if (mHeaderViewInfos.size() > 0|| mFooterViewInfos.size() > 0) {
            mAdapter = new HeaderViewListAdapter(mHeaderViewInfos, mFooterViewInfos, adapter);
        } else {
            **mAdapter = adapter;**
        }

这个if里面判断的原理？实在不懂。求指教

Answer 1

http://www.360doc.com/content/12/0401/10/3700464_199872997.shtml