Android ListView position详解及实例代码

@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;
    }

public View getView(int position, View convertView, ViewGroup parent) {
    // Header (negative positions will throw an ArrayIndexOutOfBoundsException)
    int numHeaders = getHeadersCount();
    if (position < numHeaders) {
      return mHeaderViewInfos.get(position).view;
    }

    // Adapter
    final int adjPosition = position - numHeaders;
    int adapterCount = 0;
    if (mAdapter != null) {
      adapterCount = mAdapter.getCount();
      if (adjPosition < adapterCount) {
        return mAdapter.getView(adjPosition, convertView, parent);
      }
    }

    // Footer (off-limits positions will throw an ArrayIndexOutOfBoundsException)
    return mFooterViewInfos.get(adjPosition - adapterCount).view;
  }

public Object getItem(int position) {
    // Header (negative positions will throw an ArrayIndexOutOfBoundsException)
    int numHeaders = getHeadersCount();
    if (position < numHeaders) {
      return mHeaderViewInfos.get(position).data;
    }

    // Adapter
    final int adjPosition = position - numHeaders;
    int adapterCount = 0;
    if (mAdapter != null) {
      adapterCount = mAdapter.getCount();
      if (adjPosition < adapterCount) {
        return mAdapter.getItem(adjPosition);
      }
    }

    // Footer (off-limits positions will throw an ArrayIndexOutOfBoundsException)
    return mFooterViewInfos.get(adjPosition - adapterCount).data;
  }

  public long getItemId(int position) {
    int numHeaders = getHeadersCount();
    if (mAdapter != null && position >= numHeaders) {
      int adjPosition = position - numHeaders;
      int adapterCount = mAdapter.getCount();
      if (adjPosition < adapterCount) {
        return mAdapter.getItemId(adjPosition);
      }
    }
    return -1;
  }

private class PerformClick extends WindowRunnnable implements Runnable {
    int mClickMotionPosition;

    public void run() {
      // The data has changed since we posted this action in the event queue,
      // bail out before bad things happen
      if (mDataChanged) return;

      final ListAdapter adapter = mAdapter;
      final int motionPosition = mClickMotionPosition;
      if (adapter != null && mItemCount > 0 &&
          motionPosition != INVALID_POSITION &&
          motionPosition < adapter.getCount() && sameWindow()) {
        final View view = getChildAt(motionPosition - mFirstPosition);
        // If there is no view, something bad happened (the view scrolled off the
        // screen, etc.) and we should cancel the click
        if (view != null) {
          performItemClick(view, motionPosition, adapter.getItemId(motionPosition));
        }
      }
    }
  }