附圖是錯誤日志：
該異常拋出有一定的前提：
compile 'com.android.support:recyclerview-v7:23.0.0'
RecyclerView的23版本沒有問題， 24或25版本會拋出異常。
23以上的版本中RecyclerView中的代碼已經不相同。
而23及下的RecyclerView中沒有isPreferredNextFocus方法，其focusSearch()方法內部也不一樣。高版本在focusSearch()方法內return后調用了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)) {
//此處省略N行........
if (needsFocusFailureLayout) {
//此處省略N行........
}
} else {
//此處省略N行.........
}
return isPreferredNextFocus(focused, result, direction)
? result : super.focusSearch(focused, direction);
}
需先判斷isPrfeeredNextFocus是否為true，異常在該方法內部調到的ViewGroup內部的offsetRectBetweenParentAndChild拋出異常。
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，內部又繼續調用了isPreferredNextFocusAbsolute（），內部又調用了ViewGrruop的offsetDescendantRectToMyCoords()方法,拋出異常的位置的的內部調用的ViewGruop（而此時的ViewGruop實際上是指RecyclerView）的offsetRectBetweenParentAndChild()。
接下來看一下拋出異常的位置的具體原因：
斷點在此處看一下：入參descendant是DecorView，
獲取descendant的parent時，得到的是ViewRootImpl
此時判斷descendant的parent是否是Recycler，不是，因此拋出了異常。
那么問題來了，這個方法時在做什么？
事實上這個方法是在判斷，入參中的的View，即descendant，是否是RecyclerView中的View。
通過獲取其父parent（源碼中會通過一個while循環不斷地去取parent），是否是RecyclerView，即(theParent == this），此處調用時是RecyclerView，即ViewGroup類內的this，就是指RecyclerView。
為什么得到的parent不是RecyclerView？這一定是入參descendant就已經錯了。
來看一下作者君的上層UI部分的代碼（具體還是得分析個人的上層代碼，作者君只能提供一下思路。）
處于業務需要，當時作者君重寫了LinerLayoutManager的onFocusSearchFailed()方法，指定在尋找焦點失敗的時候返回一個view。
onFocusSearchFailed()也在RecyclerView的focusSearch()內，我們來稍微回顧下：
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;
}
//此處省略N行...........
result = ff.findNextFocus(this, focused, direction);
} else {
result = ff.findNextFocus(this, focused, direction);
if (result == null && canRunFocusFailure) {
//此處省略N行.........
//可在LinerLayoutManager內重寫該方法。
result = mLayout.onFocusSearchFailed(focused, direction, mRecycler, mState);
resumeRequestLayout(false);
}
}
return isPreferredNextFocus(focused, result, direction)
? result : super.focusSearch(focused, direction);
}
作者君在尋找焦點失敗的時候，回調的這個onFocusSearchFailed內，手動返回了一個指定的View是CountLayout(即下圖中的數量這一行。)
該圖中的商品屬性：幾人坐、顏色分類是Proplayout,內部通過TextView+RecyclerView來展示商品的屬性。之所以指定是為了解決，
在顏色分類按向下鍵，需要先聚焦到數量這一行，讓用戶先選擇商品數量，但實際上卻發現,如果當前焦點在【嫩綠色[絨布]】這個屬性上時，按向下鍵時，焦點跳過數量，而跳轉到了【下單】按鈕上。因此重寫了在尋找焦點失敗的onFocusSearchFailed（）方法。因為此時RecyclerView的向下的方向上已經沒有可以聚焦的view，所以會回調此方法。而在此處指定下一個聚焦的是CountLayout(數量這一行可聚焦的view)，看起來是個不錯的解決方案。
然而由于RecyclerView高版本的源碼中在返回view時，添加了嚴格的檢查機制，需要判斷指定的view是否是RecyclerView內部的view：
return isPreferredNextFocus(focused, result, direction)
? result : super.focusSearch(focused, direction);
所以拋出了異常。
那么應該怎么做呢？為了解決向下按鍵跳行的問題，我是否應該考慮繼續在onFocusSearchFailed()內部做改動，可是這意味著還是會執行isPreferredNextFocus()，還是會拋出異常。換個方法，不讓代碼執行到這里呢？
如果了解focusSearch的源碼，你會發現一開始有個直接return的方法如下：
當onInterceptFocusSearch返回view時，后續的尋找焦點、判斷是否符合條件等等代碼都不再繼續往下執行。
public View focusSearch(View focused, int direction) {
View result = mLayout.onInterceptFocusSearch(focused, direction);
if (result != null) {
return result;
}
final FocusFinder ff = FocusFinder.getInstance();
//此處省略N行.........
return isPreferredNextFocus(focused, result, direction)
? result : super.focusSearch(focused, direction);
}
所以作者君采用重寫onInterceptFocusSearch():
具體的解決方案跟作者君的UI布局有非常大的關系，讀者需要根據自己的UI架構去更改。
? ?獲取其父view，再遍歷所有的child，如果類型是否是PropLayout，判斷其下一個是否不是PropLayout。以此獲取就是CountLayout這個child。
? ? ? ?因為作者君的布局是ScrollView內動態添加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)){
//默認設置為第1項，當countlayout內布局發生改變時，需要重新改造此段代碼
ViewGroup viewGroup=(ViewGroup) group.getChildAt(i+1);
return viewGroup;
}
}
}
}
break;
}
return super.onInterceptFocusSearch(focused, direction);
}
此處需要注意的是，如果返回的view是ViewGroup對象，其內部必須有可以獲取焦點的view，否則還是失敗的。因為在RootViewImp內會遍歷其子view，若獲取不到，就返回上一層。去尋找其他可以獲取焦點的viw。最終還是跳轉到了【下單】按鈕。
焦點查詢是從RootVieImpl進入的：
private int processKeyEvent(QueuedInputEvent q) {
final KeyEvent event = (KeyEvent)q.mEvent;
...............此處省略N行代碼，自行看源碼...............
if (direction != 0) {
View focused = mView.findFocus();
if (focused != null) {
//此處就是進入到view，再進入到Recyclerview內focusSearch的方法源頭。
View v = focused.focusSearch(direction);
if (v != null && v != focused)
//若RecyclerView內被打斷，并且返回一個View。則進入以下判斷。
focused.getFocusedRect(mTempRect);
if (mView instanceof ViewGroup) {
((ViewGroup) mView).offsetDescendantRectToMyCoords(
focused, mTempRect);
((ViewGroup) mView).offsetRectIntoDescendantCoords(
v, mTempRect);
}
//關鍵方法在這里！！！重要重要重要！！！！重要的事情說三遍
//只要這里返回true，尋找焦點則結束，那么其他view則不再有機會
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;
}
進入的標記是FOCUS_AFTER_DESCENDANTS，主要看onRequestFocusInDescendants方法返回情況，
若在這一步結束，那么就不會super。這一步進入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);
}
}
這個方法內遍歷了內部是否有可以獲取焦點的view。（因為CountLayout傳入了第2個子View，是LinearLayout，其內部的子view都不可獲取焦點，所以此方法返回了false。那么上訴代碼就變成了super，最終沒有獲取到焦點，跳轉到外部，尋找向下方向可以獲取焦點的view，最終聚焦到【下單】按鈕）
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;
}
