应公司的需求，需要在没有触摸屏只有上下确定和取消的物理按键设备上操作Recyclerview并标记出当前选中栏(多一嘴，卧槽啊，搞毛啊，省预算也不是这么省的啊！不带触摸屏你用QT啊！QT效果不好？不带触摸屏加物理按键效果就好了？！)，做的时候就想当然的在bindView里把holder添加到了集合里，然后根据上下键事件往下走改变view，然后，突然很傻比的发现忽略了最基本的事情，Recyclerview就只会在一开始创建当前屏幕显示数的holder，并不能获取到全部的holder，这样我在按下键的时候就只会走到当前显示的最后item上去，下面就再也走不动了。
好吧，开始找方法，大体思路就是动态的来获取holder改变布局，但是我需要在外面的物理按键回调里改变Recyclerview里面的view，嗯，一开始还就创建几个，后面的就不能再onBind里拿到了，再看看有没有什么其他方法，看见一个，getChildViewHolder(View child),嗯，看方法名很靠谱，但是参数是view。。。。
好吧，只能进去看看代码了，从上到下翻了一圈，发觉有一个方法
/**
* Return the ViewHolder for the item in the given position of the data set. Unlike
* {@link #findViewHolderForLayoutPosition(int)} this method takes into account any pending
* adapter changes that may not be reflected to the layout yet. On the other hand, if
* {@link Adapter#notifyDataSetChanged()} has been called but the new layout has not been
* calculated yet, this method will return <code>null</code> since the new positions of views
* are unknown until the layout is calculated.
* <p>
* This method checks only the children of RecyclerView. If the item at the given
* <code>position</code> is not laid out, it <em>will not</em> create a new one.
* <p>
* When the ItemAnimator is running a change animation, there might be 2 ViewHolders
* representing the same Item. In this case, the updated ViewHolder will be returned.
*
* @param position The position of the item in the data set of the adapter
* @return The ViewHolder at <code>position</code> or null if there is no such item
*/
public ViewHolder findViewHolderForAdapterPosition(int position) {
if (mDataSetHasChangedAfterLayout) {
return null;
}
final int childCount = mChildHelper.getUnfilteredChildCount();
// hidden VHs are not preferred but if that is the only one we find, we rather return it
ViewHolder hidden = null;
for (int i = 0; i < childCount; i++) {
final ViewHolder holder = getChildViewHolderInt(mChildHelper.getUnfilteredChildAt(i));
if (holder != null && !holder.isRemoved() && getAdapterPositionFor(holder) == position) {
if (mChildHelper.isHidden(holder.itemView)) {
hidden = holder;
} else {
return holder;
}
}
}
return hidden;
}
嗯，除了mDataSetHasChangedAfterLayout这个变量看起来有点辣眼，后面明显就可以获取到我所需要的holder啊，可以可以，来边走边试
rvPsytopicList.scrollToPosition(index);
RecyclerView.ViewHolder viewHolderForAdapterPosition = rvPsytopicList.findViewHolderForAdapterPosition(index);
先让它滑动到我所需要改变的item，更新holder，然后我获取holder该干嘛干嘛，嗯，简直天才。嗯？走到超出屏幕的下一条返回了个null？嗯？继续按走到最后再往上走就能获取到了？这玩意还有延迟不成？好吧。。再进去源码看吧。
for (int i = 0; i < childCount; i++) {
final ViewHolder holder = getChildViewHolderInt(mChildHelper.getUnfilteredChildAt(i));
//这里循环检查已存在的holder
if (holder != null && !holder.isRemoved() && getAdapterPositionFor(holder) == position) {
if (mChildHelper.isHidden(holder.itemView)) {
hidden = holder;
} else {
return holder;
}
}
}
嗯。。。。。并没有找到为啥，但是看在以上循环检查的时候debug知道以前滚过的item的holder是有的，可以，这样这个需求的难度就是不存在的了兄弟~，立马改代码，让每次多scroll一个角标，成功实现！
rvPsytopicList.scrollToPosition(index+1);
RecyclerView.ViewHolder viewHolderForAdapterPosition = rvPsytopicList.findViewHolderForAdapterPosition(index);
(初来乍到，一脚踏入不知深浅，望多多指教！)
