附图是错误日志：
image.png
该异常抛出有一定的前提：
compile 'com.android.support:recyclerview-v7:23.0.0'
RecyclerView的23版本没有问题， 24或25版本会抛出异常。
23以上的版本中RecyclerView中的代码已经不相同。
而23及下的RecyclerView中没有isPreferredNextFocus方法，其focusSearch()方法内部也不一样。高版本在focusSearch()方法内return后调用了isPreferredNextFocus()。
25版本的RecyclerView.focusSearch()
public View focusSearch(View focused, int direction) {
View result = mLayout.onInterceptFocusSearch(focused, direction);
if (result != null) {
return result;
}
final boolean canRunFocusFailure = mAdapter != null && mLayout != null
&& !isComputingLayout() && !mLayoutFrozen;
final FocusFinder ff = FocusFinder.getInstance();
if (canRunFocusFailure
&& (direction == View.FOCUS_FORWARD || direction == View.FOCUS_BACKWARD)) {
//此处省略N行........
if (needsFocusFailureLayout) {
//此处省略N行........
}
} else {
//此处省略N行.........
}
return isPreferredNextFocus(focused, result, direction)
? result : super.focusSearch(focused, direction);
}
需先判断isPrfeeredNextFocus是否为true，异常在该方法内部调到的ViewGroup内部的offsetRectBetweenParentAndChild抛出异常。
23版本的ReyclerView.focusSearch()
@Override
public View focusSearch(View focused, int direction) {
View result = mLayout.onInterceptFocusSearch(focused, direction);
if (result != null) {
return result;
}
final FocusFinder ff = FocusFinder.getInstance();
result = ff.findNextFocus(this, focused, direction);
if (result == null && mAdapter != null && mLayout != null && !isComputingLayout()
&& !mLayoutFrozen) {
eatRequestLayout();
result = mLayout.onFocusSearchFailed(focused, direction, mRecycler, mState);
resumeRequestLayout(false);
}
return result != null ? result : super.focusSearch(focused, direction);
}
高版本的isPreferredNextFocus（）方法，内部又继续调用了isPreferredNextFocusAbsolute（），内部又调用了ViewGrruop的offsetDescendantRectToMyCoords()方法,抛出异常的位置的的内部调用的ViewGruop（而此时的ViewGruop实际上是指RecyclerView）的offsetRectBetweenParentAndChild()。
接下来看一下抛出异常的位置的具体原因：
断点在此处看一下：入参descendant是DecorView，
image
获取descendant的parent时，得到的是ViewRootImpl
image
此时判断descendant的parent是否是Recycler，不是，因此抛出了异常。
那么问题来了，这个方法时在做什么？
事实上这个方法是在判断，入参中的的View，即descendant，是否是RecyclerView中的View。
通过获取其父parent（源码中会通过一个while循环不断地去取parent），是否是RecyclerView，即(theParent == this），此处调用时是RecyclerView，即ViewGroup类内的this，就是指RecyclerView。
为什么得到的parent不是RecyclerView？这一定是入参descendant就已经错了。
来看一下作者君的上层UI部分的代码（具体还是得分析个人的上层代码，作者君只能提供一下思路。）
处于业务需要，当时作者君重写了LinerLayoutManager的onFocusSearchFailed()方法，指定在寻找焦点失败的时候返回一个view。
image
onFocusSearchFailed()也在RecyclerView的focusSearch()内，我们来稍微回顾下：
public View focusSearch(View focused, int direction) {
View result = mLayout.onInterceptFocusSearch(focused, direction);
if (result != null) {
return result;
}
final FocusFinder ff = FocusFinder.getInstance();
if (canRunFocusFailure
&& (direction == View.FOCUS_FORWARD ||
direction == View.FOCUS_BACKWARD)) {
boolean needsFocusFailureLayout = false;
if (mLayout.canScrollVertically()) {
final int absDir =
direction == View.FOCUS_FORWARD ? View.FOCUS_DOWN : View.FOCUS_UP;
final View found = ff.findNextFocus(this, focused, absDir);
needsFocusFailureLayout = found == null;
}
//此处省略N行...........
result = ff.findNextFocus(this, focused, direction);
} else {
result = ff.findNextFocus(this, focused, direction);
if (result == null && canRunFocusFailure) {
//此处省略N行.........
//可在LinerLayoutManager内重写该方法。
result = mLayout.onFocusSearchFailed(focused, direction, mRecycler, mState);
resumeRequestLayout(false);
}
}
return isPreferredNextFocus(focused, result, direction)
? result : super.focusSearch(focused, direction);
}
作者君在寻找焦点失败的时候，回调的这个onFocusSearchFailed内，手动返回了一个指定的View是CountLayout(即下图中的数量这一行。)
该图中的商品属性：几人坐、颜色分类是Proplayout,内部通过TextView+RecyclerView来展示商品的属性。之所以指定是为了解决，
在颜色分类按向下键，需要先聚焦到数量这一行，让用户先选择商品数量，但实际上却发现,如果当前焦点在【嫩绿色[绒布]】这个属性上时，按向下键时，焦点跳过数量，而跳转到了【下单】按钮上。因此重写了在寻找焦点失败的onFocusSearchFailed（）方法。因为此时RecyclerView的向下的方向上已经没有可以聚焦的view，所以会回调此方法。而在此处指定下一个聚焦的是CountLayout(数量这一行可聚焦的view)，看起来是个不错的解决方案。
image.png
然而由于RecyclerView高版本的源码中在返回view时，添加了严格的检查机制，需要判断指定的view是否是RecyclerView内部的view：
return isPreferredNextFocus(focused, result, direction)
? result : super.focusSearch(focused, direction);
所以抛出了异常。
那么应该怎么做呢？为了解决向下按键跳行的问题，我是否应该考虑继续在onFocusSearchFailed()内部做改动，可是这意味着还是会执行isPreferredNextFocus()，还是会抛出异常。换个方法，不让代码执行到这里呢？
如果了解focusSearch的源码，你会发现一开始有个直接return的方法如下：
当onInterceptFocusSearch返回view时，后续的寻找焦点、判断是否符合条件等等代码都不再继续往下执行。
public View focusSearch(View focused, int direction) {
View result = mLayout.onInterceptFocusSearch(focused, direction);
if (result != null) {
return result;
}
final FocusFinder ff = FocusFinder.getInstance();
//此处省略N行.........
return isPreferredNextFocus(focused, result, direction)
? result : super.focusSearch(focused, direction);
}
所以作者君采用重写onInterceptFocusSearch():
具体的解决方案跟作者君的UI布局有非常大的关系，读者需要根据自己的UI架构去更改。
获取其父view，再遍历所有的child，如果类型是否是PropLayout，判断其下一个是否不是PropLayout。以此获取就是CountLayout这个child。
因为作者君的布局是ScrollView内动态添加PropLayout（TextView+RecyclerView）和CountLayout
inearLayoutManager=new LinearLayoutManager(mContext){
@Override
public View onInterceptFocusSearch(View focused, int direction) {
switch (direction){
case View.FOCUS_DOWN:
if (getParent() instanceof ViewGroup){
ViewGroup group= (ViewGroup) getParent();
for (int i=0;i<group.getChildCount();i++){
if (group.getChildAt(i)==PropLayout.this){
if (i+1<group.getChildCount()&&!(group.getChildAt(i+1) instanceof PropLayout)){
//默认设置为第1项，当countlayout内布局发生改变时，需要重新改造此段代码
ViewGroup viewGroup=(ViewGroup) group.getChildAt(i+1);
return viewGroup;
}
}
}
}
break;
}
return super.onInterceptFocusSearch(focused, direction);
}
此处需要注意的是，如果返回的view是ViewGroup对象，其内部必须有可以获取焦点的view，否则还是失败的。因为在RootViewImp内会遍历其子view，若获取不到，就返回上一层。去寻找其他可以获取焦点的viw。最终还是跳转到了【下单】按钮。
焦点查询是从RootVieImpl进入的：
private int processKeyEvent(QueuedInputEvent q) {
final KeyEvent event = (KeyEvent)q.mEvent;
...............此处省略N行代码，自行看源码...............
if (direction != 0) {
View focused = mView.findFocus();
if (focused != null) {
//此处就是进入到view，再进入到Recyclerview内focusSearch的方法源头。
View v = focused.focusSearch(direction);
if (v != null && v != focused)
//若RecyclerView内被打断，并且返回一个View。则进入以下判断。
focused.getFocusedRect(mTempRect);
if (mView instanceof ViewGroup) {
((ViewGroup) mView).offsetDescendantRectToMyCoords(
focused, mTempRect);
((ViewGroup) mView).offsetRectIntoDescendantCoords(
v, mTempRect);
}
//关键方法在这里！！！重要重要重要！！！！重要的事情说三遍
//只要这里返回true，寻找焦点则结束，那么其他view则不再有机会
if (v.requestFocus(direction, mTempRect)) {
playSoundEffect(SoundEffectConstants
.getContantForFocusDirection(direction));
return FINISH_HANDLED;
}
}
// Give the focused view a last chance to handle the dpad key.
if (mView.dispatchUnhandledMove(focused, direction)) {
return FINISH_HANDLED;
}
} else {
// find the best view to give focus to in this non-touch-mode with no-focus
View v = focusSearch(null, direction);
if (v != null && v.requestFocus(direction)) {
return FINISH_HANDLED;
}
}
}
}
return FORWARD;
}
进入的标记是FOCUS_AFTER_DESCENDANTS，主要看onRequestFocusInDescendants方法返回情况，
若在这一步结束，那么就不会super。这一步进入ViewGroup的requestFocus()方法。
public boolean requestFocus(int direction, Rect previouslyFocusedRect) {
if (DBG) {
System.out.println(this + " ViewGroup.requestFocus direction="
+ direction);
}
int descendantFocusability = getDescendantFocusability();
switch (descendantFocusability) {
case FOCUS_BLOCK_DESCENDANTS:
return super.requestFocus(direction, previouslyFocusedRect);
case FOCUS_BEFORE_DESCENDANTS: {
final boolean took = super.requestFocus(direction, previouslyFocusedRect);
return took ? took : onRequestFocusInDescendants(direction, previouslyFocusedRect);
}
case FOCUS_AFTER_DESCENDANTS: {
final boolean took = onRequestFocusInDescendants(direction, previouslyFocusedRect);
return took ? took : super.requestFocus(direction, previouslyFocusedRect);
}
default:
throw new IllegalStateException("descendant focusability must be "
+ "one of FOCUS_BEFORE_DESCENDANTS, FOCUS_AFTER_DESCENDANTS, FOCUS_BLOCK_DESCENDANTS "
+ "but is " + descendantFocusability);
}
}
这个方法内遍历了内部是否有可以获取焦点的view。（因为CountLayout传入了第2个子View，是LinearLayout，其内部的子view都不可获取焦点，所以此方法返回了false。那么上诉代码就变成了super，最终没有获取到焦点，跳转到外部，寻找向下方向可以获取焦点的view，最终聚焦到【下单】按钮）
protected boolean onRequestFocusInDescendants(int direction,
Rect previouslyFocusedRect) {
int index;
int increment;
int end;
int count = mChildrenCount;
if ((direction & FOCUS_FORWARD) != 0) {
index = 0;
increment = 1;
end = count;
} else {
index = count - 1;
increment = -1;
end = -1;
}
final View[] children = mChildren;
for (int i = index; i != end; i += increment) {
View child = children[i];
if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE) {
if (child.requestFocus(direction, previouslyFocusedRect)) {
return true;
}
}
}
return false;
}
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