RecyclerView 在 onLayout 的时候 会报崩溃异常

Question

recyclerview 我默认加载了2个布局 , mChildHelper.getChildCount() == 2
但是在 onlayout -- > dispatchLayoutStep1 --->findMinMaxChildLayoutPositions 方法里面 final ViewHolder holder = getChildViewHolderInt(mChildHelper.getChildAt(i)) 是个空指针

java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.support.v7.widget.RecyclerView$ViewHolder.shouldIgnore()' on a null object reference
    at android.support.v7.widget.RecyclerView.findMinMaxChildLayoutPositions(RecyclerView.java:3757)
    at android.support.v7.widget.RecyclerView.dispatchLayoutStep1(RecyclerView.java:3494)
    at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:3310)
    at android.support.v7.widget.RecyclerView.onLayout(RecyclerView.java:3844)
    at android.view.View.layout(View.java:16653)
    at android.view.ViewGroup.layout(ViewGroup.java:5438)
    at android.support.v4.widget.SwipeRefreshLayout.onLayout(SwipeRefreshLayout.java:636)
    at android.view.View.layout(View.java:16653)
    at android.view.ViewGroup.layout(ViewGroup.java:5438)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:336)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:273)
    at android.view.View.layout(View.java:16653)
    at android.view.ViewGroup.layout(ViewGroup.java:5438)
    at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1743)
    at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1586)
    at android.widget.LinearLayout.onLayout(LinearLayout.java:1495)
    at android.view.View.layout(View.java:16653)
    at android.view.ViewGroup.layout(ViewGroup.java:5438)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:336)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:273)
    at android.view.View.layout(View.java:16653)
    at android.view.ViewGroup.layout(ViewGroup.java:5438)
    at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1080)
    at android.view.View.layout(View.java:16653)
    at android.view.ViewGroup.layout(ViewGroup.java:5438)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:336)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:273)
    at android.view.View.layout(View.java:16653)
    at android.view.ViewGroup.layout(ViewGroup.java:5438)
    at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1743)
    at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1586)
    at android.widget.LinearLayout.onLayout(LinearLayout.java:1495)
    at android.view.View.layout(View.java:16653)
    at android.view.ViewGroup.layout(ViewGroup.java:5438)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:336)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:273)
    at android.view.View.layout(View.java:16653)
    at android.view.ViewGroup.layout(ViewGroup.java:5438)
    at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1743)
    at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1586)
    at android.widget.LinearLayout.onLayout(LinearLayout.java:1495)
    at android.view.View.layout(View.java:16653)
    at android.view.ViewGroup.layout(ViewGroup.java:5438)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:336)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:273)
    at android.view.View.layout(View.java:16653)
    at android.view.ViewGroup.layout(ViewGroup.java:5438)
    at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1743)
    at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1586)
    at android.widget.LinearLayout.onLayout(LinearLayout.java:1495)
    at android.view.View.layout(View.java:16653)
    at android.view.ViewGroup.layout(ViewGroup.java:5438)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:336)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:273)
    at com.android.internal.policy.PhoneWindow$DecorView.onLayout(PhoneWindow.java:2680)
    at android.view.View.layout(View.java:16653)
    at android.view.ViewGroup.layout(ViewGroup.java:5438)
    at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2214)
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1974)
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1150)
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6061)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:860)
    at android.view.Choreographer.doCallbacks(Choreographer.java:672)
    at android.view.Choreographer.doFrame(Choreographer.java:608)
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:846)
    at android.os.Handler.handleCallback(Handler.java:739)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:148)
    at android.app.ActivityThread.main(ActivityThread.java:5458)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628)