关于listview

1、listview 设置stackFromBottom="true" 这个属性以后，item会从底部向顶部 排列，

/**
     * Make sure views are touching the top or bottom edge, as appropriate for
     * our gravity
     */
    private void adjustViewsUpOrDown() {
        final int childCount = getChildCount();
        int delta;


        if (childCount > 0) {
            View child;


            if (!mStackFromBottom) {
                // Uh-oh -- we came up short. Slide all views up to make them
                // align with the top
                child = getChildAt(0);
                delta = child.getTop() - mListPadding.top;
                if (mFirstPosition != 0) {
                    // It's OK to have some space above the first item if it is
                    // part of the vertical spacing
                    delta -= mDividerHeight;
                }
                if (delta < 0) {
                    // We only are looking to see if we are too low, not too high
                    delta = 0;
                }
            } else {
                // we are too high, slide all views down to align with bottom
                child = getChildAt(childCount - 1);
                delta = child.getBottom() - (getHeight() - mListPadding.bottom);


                if (mFirstPosition + childCount < mItemCount) {
                    // It's OK to have some space below the last item if it is
                    // part of the vertical spacing
                    delta += mDividerHeight;
                }


                if (delta > 0) {
                    delta = 0;
                }
            }


            if (delta != 0) {
                offsetChildrenTopAndBottom(-delta);
            }
        }
    }

最后到了viewgroup里边 调用的这个方法

public void offsetChildrenTopAndBottom(int offset) {
        final int count = mChildrenCount;
        final View[] children = mChildren;


        for (int i = 0; i < count; i++) {
            final View v = children[i];
            v.mTop += offset;
            v.mBottom += offset;
        }
    }

重新设置位置

2、关于 addHeadView

代码445行

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

如果有headview或者footview，就会用HeaderViewListAdapter去包装我们设置的adapter。

看他的getCount方法

public int getCount() {
        if (mAdapter != null) {
            return getFootersCount() + getHeadersCount() + mAdapter.getCount();
        } else {
            return getFootersCount() + getHeadersCount();
        }
    }

设置onitemclicklistener以后

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));
                }
            }
        }
    }

如果 有head或者footer，mAdapter 就是HeaderViewListAdapter，所以，onitemclicklistener 这里可以得到head或者footer的点击事件。