当展开或者收起时会激发这个函数，其中结构指针pNMTreeView的action参数，就记录了是打开还是关闭，即 if(pNMTreeView-> action == 1) //设置收起的图标； else if(pNMTreeView-> action == 2) //设置展开后的图标； -When you expand or hide, can trigger this function, in which the action parameter structure pointer pNMTreeView, on the record is open or closed, ie if (pNMTreeView->　action == 1)// Set the icon away　else if (pNMTreeView->　action == 2)// set the Expand icon