RecycleView在片段中崩溃，因为LayoutManager是NULL

Question

我有三个选项卡谁都在tablayout，在Tab1中，有一个RecycleView。

今天我想SwipeRefreshLayout添加到它：

<android.support.v4.widget.SwipeRefreshLayout 
    android:id="@+id/swiperefreshlayout" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent"> 

    <android.support.v7.widget.RecyclerView 
     android:id="@+id/recyclerView" 
     android:layout_width="match_parent" 
     android:layout_height="match_parent"> 
    </android.support.v7.widget.RecyclerView> 

</android.support.v4.widget.SwipeRefreshLayout> 

在Tab1Fragment：

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
         Bundle savedInstanceState) { 
    View view = inflater.inflate(R.layout.activity_main_list, container, false); 
    recyclerView = (RecyclerView) view.findViewById(R.id.recyclerView); 
    staggeredGridLayoutManager = new StaggeredGridLayoutManager(3, StaggeredGridLayoutManager.VERTICAL); 
    recyclerView.setLayoutManager(staggeredGridLayoutManager); 
    swipeRefreshLayout = (SwipeRefreshLayout) view.findViewById(R.id.swiperefreshlayout); 
    swipeRefreshLayout.setColorSchemeResources(android.R.color.holo_blue_bright, android.R.color.holo_green_light, 
      android.R.color.holo_orange_light, android.R.color.holo_red_light); 
    return view; 
} 

不幸的是，当我从TAB1到TAB2滚动，然后回到TAB1，活动崩溃：

java.lang.NullPointerException: Attempt to invoke virtual method 'boolean 
android.support.v7.widget.RecyclerView$LayoutManager.canScrollVertically()' on a null object reference 
    at android.support.v7.widget.RecyclerView.computeVerticalScrollOffset(RecyclerView.java:1613) 
    at android.view.View.canScrollVertically(View.java:12880) 

但很明显，我已经设置了LayoutManger！看来，在staggeredgridlayout走了......

更重要的是Weired的是，当我只需点击TAB1，TAB2，活动不会崩溃，但是，当我从TAB2滚动到TAB1，它坠毁

发生了什么？谢谢！

PLUS整个错误日志：

12-02 16:57:59.857 28189-28189/xyz.doutu.doutu E/AndroidRuntime: Process: xyz.doutu.doutu, PID: 28189 
     ava.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.support.v7.widget.RecyclerView$LayoutManager.canScrollVertically()' on a null object reference 
    at android.support.v7.widget.RecyclerView.computeVerticalScrollOffset(RecyclerView.java:1613) 
    at android.view.View.canScrollVertically(View.java:12880) 
    at android.support.v4.view.ViewCompatICS.canScrollVertically(ViewCompatICS.java:35) 
    at android.support.v4.view.ViewCompat$ICSViewCompatImpl.canScrollVertically(ViewCompat.java:1253) 
    at android.support.v4.view.ViewCompat.canScrollVertically(ViewCompat.java:1695) 
    at android.support.v4.widget.SwipeRefreshLayout.canChildScrollUp(SwipeRefreshLayout.java:646) 
    at android.support.v4.widget.SwipeRefreshLayout.onInterceptTouchEvent(SwipeRefreshLayout.java:660) 
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1961) 
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2408) 
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2050) 
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2408) 
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2050) 
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2408) 
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2050) 
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2408) 
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2050) 
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2408) 
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2050) 
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2408) 
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2050) 
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2408) 
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2050) 
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2408) 
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2050) 
    at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2390) 
    at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1734) 
    at android.app.Activity.dispatchTouchEvent(Activity.java:2833) 
    at android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:60) 
    at android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:60) 
    at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2351) 
    at android.view.View.dispatchPointerEvent(View.java:8700) 

Answer 1

移动你的recyclerView分配onViewCreated()而不是onCreateView()。问题是当您的TabFragment被viewPager滚动分离并重新附加时。