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

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 position         * has been removed from the data set. The items previously located at and after         * position may now be found at oldPosition - 1.         *         * 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.
         *         * @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 position         * has been newly inserted. The item previously at position is now at         * position position + 1.         *         * 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.
         *         * @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 fromPosition         * has been moved to toPosition.         *         * 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.
         *         * @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

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