RecyclerView采坑记录

1.在调用Adapter的notifyDataSetChanged后，看下面代码的注释：

/**
 * Notify any registered observers that the data set has changed.
 *
 * <p>There are two different classes of data change events, item changes and structural
 * changes. Item changes are when a single item has its data updated but no positional
 * changes have occurred. Structural changes are when items are inserted, removed or moved
 * within the data set.</p>
 *
 * <p>This event does not specify what about the data set has changed, forcing
 * any observers to assume that all existing items and structure may no longer be valid.
 * LayoutManagers will be forced to fully rebind and relayout all visible views.</p>
 *
 * <p><code>RecyclerView</code> will attempt to synthesize visible structural change events
 * for adapters that report that they have {@link #hasStableIds() stable IDs} when
 * this method is used. This can help for the purposes of animation and visual
 * object persistence but individual item views will still need to be rebound
 * and relaid out.</p>
 *
 * <p>If you are writing an adapter it will always be more efficient to use the more
 * specific change events if you can. Rely on <code>notifyDataSetChanged()</code>
 * as a last resort.</p>
 *
 * @see #notifyItemChanged(int)
 * @see #notifyItemInserted(int)
 * @see #notifyItemRemoved(int)
 * @see #notifyItemRangeChanged(int, int)
 * @see #notifyItemRangeInserted(int, int)
 * @see #notifyItemRangeRemoved(int, int)
 */
public final void notifyDataSetChanged() {
    mObservable.notifyChanged();
}

可以看出，在调用notifyDataSetChanged后，调用Recyclerview的getChildAdapterPosition(view)就会返回-1，这时要使用getChildLayoutPosition(view)可以拿到layout之前的对应view的位置，getChildAdapterPosition(view)和getChildLayoutPosition(view)本质上调用的是ViewHolder的getAdapterPosition()和getLayoutPosition()方法。二者区别如下：

(1)getLayoutPosition()：返回的一直是界面上呈现的 Item 的位置信息，即使某个 Item 已经从数据源中被移除。

(2)getAdapterPosition()：当数据源发生变化，且界面已经刷新过后即 onBindViewHolder() 已经被调用了后，返回的值跟 getLayoutPosition() 一致；但当数据源发生变化，且在 onBindViewHolder() 被调用之前，如果调用了 notifyDataSetChanged(), 那么将返回无效的位置标志 -1；如果调用了 notifyItem系列()，那么将返回 Item 在数据源中的位置信息。