RecyclerView的notifyItemRemoved()方法删除条目问题

     在使用RecyclerView进行开发时，使用notifyItemRemoved()方法删除条目和notifyItemMoved()方法移动条目，遇到删除和移动的条目出现紊乱。

      1.删除

      

本来是删除条目3，没想到结果却是删除了条目4。

    在RecyclerView中，并没有提供条目点击监听接口，所以只得在  public void onBindViewHolder(final RecyclerView.ViewHolder holder, final int position)方法中通过holder.itemView.setOnLongClickListener()和holder.itemView.setOnClickListener()来监听条目长按和点击事件，关于点击的条目位置是通过参数position来确定的，查看onBindViewHolder()方法的注释：

   /**
         * Called by RecyclerView to display the data at the specified position. This method
         * should update the contents of the {@link ViewHolder#itemView} to reflect the item at
         * the given position.
         * 

         * Note that unlike {@link android.widget.ListView}, RecyclerView will not call this
         * method again if the position of the item changes in the data set unless the item itself
         * is invalidated or the new position cannot be determined. For this reason, you should only
         * use the position parameter while acquiring the related data item inside this
         * method and should not keep a copy of it. If you need the position of an item later on
         * (e.g. in a click listener), use {@link ViewHolder#getPosition()} which will have the
         * updated position.
         *
         * @param holder The ViewHolder which should be updated to represent the contents of the
         *               item at the given position in the data set.
         * @param position The position of the item within the adapter's data set.
         */
        public abstract void onBindViewHolder(VH holder, int position);

从中知道，如果需要监听条目点击的事件，使用ViewHolder的getLayoutPosition()（getPosition()被抛弃）方法才能获得更新后的条目位置，因此：

 holder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                holder.getPosition();//not position
            }
        });

传入的条目位置索引应该使用getLayoutPosition()（getPosition()被抛弃）方法来获取，这样就不会出现条目紊乱。

       2.置顶

       
置顶之后，再滑动，条目变回原来的顺序，查看notifyItemMoved()方法的注释：

 /**
         * 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);
        }

尽管条目的位置改变了，但是数据集仍然不会改变，因此需要改变数据集，才能让条目的位置真正改变。

 int position = holder.getPosition();
                    String object = mDatas.get(position);
                    mDatas.remove(position);
                    mDatas.add(0,object);
                    notifyItemMoved(position, 0);