Android RecyclerView单点、批量数据元素项目item的增加、删除和移动

前文附录1,2介绍了基本的Android RecyclerView单点、批量元素项目的更新。现在给出其他比较重要的Android RecyclerView数据元素项目的删除和增加，删除和增加包含两种，一种是单点，另外一种是批量的元素。

（一）RecyclerView删除操作。

（a）单点删除：notifyItemRemoved(int position)

 /**
         * Notify any registered observers that the item previously located at <code>position</code>
         * has been removed from the data set. The items previously located at and after
         * <code>position</code> may now be found at <code>oldPosition - 1</code>.
         *
         * <p>This is a structural change event. Representations of other existing items in the
         * data set are still considered up to date and will not be rebound, though their positions
         * may be altered.</p>
         *
         * @param position Position of the item that has now been removed
         *
         * @see #notifyItemRangeRemoved(int, int)
         */
        public final void notifyItemRemoved(int position) {
            mObservable.notifyItemRangeRemoved(position, 1);
        }

在给adapter维持的数据队列删除一个元素后，调用此方法，该方法删除指定位置position的元素并更新RecyclerView。

（b）批量删除：notifyItemRangeRemoved(int positionStart, int itemCount) 

 public void notifyItemRangeRemoved(int positionStart, int itemCount) {
            // since onItemRangeRemoved() is implemented by the app, it could do anything, including
            // removing itself from {@link mObservers} - and that could cause problems if
            // an iterator is used on the ArrayList {@link mObservers}.
            // to avoid such problems, just march thru the list in the reverse order.
            for (int i = mObservers.size() - 1; i >= 0; i--) {
                mObservers.get(i).onItemRangeRemoved(positionStart, itemCount);
            }
        }

在给adapter维持的数据元素队列批量删除若干元素后，调用该方法，该方法删除从开始位置positionStart起之后的itemCount个数量的子元素，然后更新RecyclerView。


（二）RecyclerView增加操作。

（a）单点增加：notifyItemInserted(int position)

/**
         * Notify any registered observers that the item reflected at <code>position</code>
         * has been newly inserted. The item previously at <code>position</code> is now at
         * position <code>position + 1</code>.
         *
         * <p>This is a structural change event. Representations of other existing items in the
         * data set are still considered up to date and will not be rebound, though their
         * positions may be altered.</p>
         *
         * @param position Position of the newly inserted item in the data set
         *
         * @see #notifyItemRangeInserted(int, int)
         */
        public final void notifyItemInserted(int position) {
            mObservable.notifyItemRangeInserted(position, 1);
        }

在给adapter指定位置position增加一个元素后，调用notifyItemInserted方法，更新RecyclerView。

（b）批量增加：notifyItemRangeInserted(int positionStart, int itemCount)

public void notifyItemRangeInserted(int positionStart, int itemCount) {
            // since onItemRangeInserted() is implemented by the app, it could do anything,
            // including removing itself from {@link mObservers} - and that could cause problems if
            // an iterator is used on the ArrayList {@link mObservers}.
            // to avoid such problems, just march thru the list in the reverse order.
            for (int i = mObservers.size() - 1; i >= 0; i--) {
                mObservers.get(i).onItemRangeInserted(positionStart, itemCount);
            }
        }

在给adapter适配器指定位置positionStart增加itemCount个数据元素后，调用此方法，更新RecyclerView。

（三）RecyclerView移动操作。

notifyItemMoved(int fromPosition, int toPosition)

 /**
         * Notify any registered observers that the item reflected at <code>fromPosition</code>
         * has been moved to <code>toPosition</code>.
         *
         * <p>This is a structural change event. Representations of other existing items in the
         * data set are still considered up to date and will not be rebound, though their
         * positions may be altered.</p>
         *
         * @param fromPosition Previous position of the item.
         * @param toPosition New position of the item.
         */
        public final void notifyItemMoved(int fromPosition, int toPosition) {
            mObservable.notifyItemMoved(fromPosition, toPosition);
        }

移动操作的对象位置有两个，开始对象位置fromPosition和目的地址位置toPosition。设定这两个位置后，fromPosition元素位置的元素被移动到toPosition。fromPosition和toPosition是元素的集合队列中的下标。

附录：
1，《 Android RecyclerView更新子项目notifyItemChanged》链接：http://blog.csdn.net/zhangphil/article/details/78565738 
2，《Android RecyclerView批量更新notifyItemRangeChanged》链接：http://blog.csdn.net/zhangphil/article/details/78579849