Android--ExpandbleView源码学习----ExpandableListPosition类-优快云博客

本文深入探讨了ExpandableListPosition类在Android列表适配器中的使用方式，包括如何获取子项和组项的位置以及通过位操作表示它们的位置。详细解释了类的成员方法和实例化过程，提供了实际应用示例。

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Class OverView

ExpandbaleListPosition类可以指向group的位置或则child的位置。可通过obtainChildPosition(int,int)和obtainGroupPosition(int)获得实例

/***根据type返回groupPosition或则childPosition的格式为64位的数据**/long getPackedPosition() { if (type == CHILD) return ExpandableListView.getPackedPositionForChild(groupPos, childPos); else return ExpandableListView.getPackedPositionForGroup(groupPos); }//static ExpandableListPosition obtain(int type, int groupPos, int childPos, int flatListPos) { ExpandableListPosition elp = getRecycledOrCreate(); elp.type = type; elp.groupPos = groupPos; elp.childPos = childPos; elp.flatListPos = flatListPos; return elp; }

//初始化对象

private void resetState() { groupPos = 0; childPos = 0; flatListPos = 0; type = 0; }

//返回一个ExpandableListPosition，如果池中有对象则返回池中对象并且移除该对象（将被初始化），如果没有则新new一个对象返回 private static ExpandableListPosition getRecycledOrCreate() { ExpandableListPosition elp; synchronized (sPool) { if (sPool.size() > 0) { elp = sPool.remove(0); } else { return new ExpandableListPosition(); } } elp.resetState(); return elp; }//增加一个ExpandableListPosition对象到池中

public void recycle() {
        synchronized (sPool) {
            if (sPool.size() < MAX_POOL_SIZE) {
                sPool.add(this);
            }
        }
    }

//获得一个ExpandableListPosition对象

static ExpandableListPosition obtain(int type, int groupPos, int childPos, int flatListPos) { ExpandableListPosition elp = getRecycledOrCreate(); elp.type = type; elp.groupPos = groupPos; elp.childPos = childPos; elp.flatListPos = flatListPos; return elp; } //获得一个group类型的ExpandableListPosition对象static ExpandableListPosition obtainGroupPosition(int groupPosition) { return obtain(GROUP, groupPosition, 0, 0); }

//获得一个child类型的ExpandableListPosition对象   
 static ExpandableListPosition obtainChildPosition(int groupPosition, int childPosition) { return obtain(CHILD, groupPosition, childPosition, 0); }

//根据位置的封装数据得到位置的ExpandbaleListPostion static ExpandableListPosition obtainPosition(long packedPosition) { if (packedPosition == ExpandableListView.PACKED_POSITION_VALUE_NULL) { return null; } ExpandableListPosition elp = getRecycledOrCreate(); elp.groupPos = ExpandableListView.getPackedPositionGroup(packedPosition); if (ExpandableListView.getPackedPositionType(packedPosition) == ExpandableListView.PACKED_POSITION_TYPE_CHILD) { elp.type = CHILD; elp.childPos = ExpandableListView.getPackedPositionChild(packedPosition); } else { elp.type = GROUP; } return elp; }