RecyclerView在滚动上崩溃

问题描述：

我有一些图像排列在水平网格中。我想使用关键事件从左到右和从右到左移动我的网格。当我通过网格移动时，发生了两件事RecyclerView在滚动上崩溃

选择了第二个位置的项目。例如，我处于位置0并想要选择位置1处的下一个项目，但我的网格选择位置2项目并跳过位置1项目。

上滚动我得到空指针异常

if(keyCode == KeyEvent.KEYCODE_DPAD_RIGHT) 
    { 
    if (mCurrentSelectedPosition + 1 < getItemCount()) { 
    Log.e("current position1",Integer.toString(mCurrentSelectedPosition)); 

    gridHolder = (GridView_Holder) mRecyclerView.findViewHolderForPosition(mCurrentSelectedPosition); 
    gridHolder.itemView.setSelected(false); 
    notifyItemChanged(mCurrentSelectedPosition); 
    notifyDataSetChanged(); 

    int lastItem = lm.findLastCompletelyVisibleItemPosition(); 
    Log.e("last item",Integer.toString(lastItem)); 

    if ((mCurrentSelectedPosition + 1) > lastItem) { 
     // Log.e("Is less", "true"); 
     recyclerView.smoothScrollToPosition(mCurrentSelectedPosition + 1); 
     Log.e("current position2",Integer.toString(mCurrentSelectedPosition)); 

    } else { 
     gridHolder = (GridView_Holder) mRecyclerView.findViewHolderForPosition(mCurrentSelectedPosition + 1); 
     gridHolder.itemView.setSelected(true); 
     Log.e("current position3",Integer.toString(mCurrentSelectedPosition)); 
    } 

    mCurrentSelectedPosition += 1; 
    Log.e("current position4",Integer.toString(mCurrentSelectedPosition)); 
} 
return true; 
}

滚动收听

gridRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener(){ 
     @Override 
     public void onScrolled(RecyclerView recyclerView, int x, int y) 
     { 
      super.onScrolled(recyclerView, x, y); 
      try { 
       GridView_Holder gridHolder; 
       gridHolder= (GridView_Holder) recyclerView.findViewHolderForPosition(adapter.mCurrentSelectedPosition); 

       gridHolder.itemView.setSelected(true); 
      }catch(Exception e){ 
       Log.e("exception",e.getMessage()); 
      } 

     }

这是我的logcat

java.lang.NullPointerException: Attempt to read from field 'android.view.View android.support.v7.widget.RecyclerView$ViewHolder.itemView' on a null object reference 
at com.winettv.recylcerviewwithdpad.GridView_Recycler_Adapter$1.onKey(GridView_Recycler_Adapter.java:193) 
at android.view.View.dispatchKeyEvent(View.java:9230) 
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1635) 
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1640) 
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1640) 
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1640) 
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1640) 
at android.widget.ScrollView.dispatchKeyEvent(ScrollView.java:379) 
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1640) 
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1640) 
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1640) 
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1640) 
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1640) 
at com.android.internal.policy.PhoneWindow$DecorView.superDispatchKeyEvent(PhoneWindow.java:2395) 
at com.android.internal.policy.PhoneWindow.superDispatchKeyEvent(PhoneWindow.java:1727) 
at android.app.Activity.dispatchKeyEvent(Activity.java:2725) 
at android.support.v7.app.AppCompatActivity.dispatchKeyEvent(AppCompatActivity.java:543) 
at android.support.v7.view.WindowCallbackWrapper.dispatchKeyEvent(WindowCallbackWrapper.java:53) 
at android.support.v7.app.AppCompatDelegateImplBase$AppCompatWindowCallbackBase.dispatchKeyEvent(AppCompatDelegateImplBase.java:315)

[findViewHolderForPosition]（https://developer.android.com/reference/android/support/v7/widget/RecyclerView.html#findViewHolderForPosition（INT））已被弃用，你试图与[findViewHolderForAdapterPosition替换它]（https://developer.android.com/reference/android/support/v7/widget/RecyclerView.html#findViewHolderForAdapterPosition（INT））？ – Rehan

答

当我在滚动期间开发了定制翻译库我有同样的问题。只有在快速滚动时，当我试图从列表中访问视图元素时，这是空的，这里是NPE。

所以有一个非常简单的解决方法，就是跳过空的元素，然后继续添加新的元素。在我的情况是这样的：

// Other init.... 
for (int i = 0; i < MainListView.getChildCount; i++) { 
    if (MainListView.getChildAt(i) == null) 
     continue; 
    // Continue base behavior 
}

出现这种情况的基础上，滚动型（这是RecycleView，ListView控件，等父母）当我们试图访问查看现在正在重绘。无论如何，只是简单的空检查应该可以解决你的问题。

更新1：

还可根据RecyclerView缓存视图布局，则需要另一种选择。见下文。

gridRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener(){ 
     @Override 
     public void onScrolled(RecyclerView recyclerView, int x, int y) 
     { 
      super.onScrolled(recyclerView, x, y); 
      GridView_Holder gridHolder; 
      gridHolder= (GridView_Holder) recyclerView.findViewHolderForPosition(adapter.mCurrentSelectedPosition); 
      if (gridHolder != null && gridHolder.itemView != null) { 
        gridHolder.itemView.setSelected(true); 
      } 
     } 
}

我滚动时崩溃。我添加了onScrollListener的代码。请检查。 – Andrain

答

在代码GR idHolder.itemView.setSelected（真）; gridHolder为null。

更改这样的代码并尝试。

if ((mCurrentSelectedPosition + 1) > lastItem) { 
     // Log.e("Is less", "true"); 
     recyclerView.smoothScrollToPosition(mCurrentSelectedPosition); 
     Log.e("current position2",Integer.toString(mCurrentSelectedPosition)); 

    } else { 
     gridHolder = (GridView_Holder) mRecyclerView.findViewHolderForPosition(mCurrentSelectedPosition); 
     gridHolder.itemView.setSelected(true); 
     Log.e("current position3",Integer.toString(mCurrentSelectedPosition)); 
    }

坠机原因。

这并没有解决我的问题我仍然面临同样的崩溃 – Andrain

答

按该错误很明显，

(GridView_Holder)mRecyclerView.findViewHolderForPosition(mCurrentSelectedPosition);

为空。这是造成这次事故的原因。

您可以参考以下链接

FindViewHolderForPosition return null when card's not in vision

RecyclerView - findViewHolderForPosition always returns null when onBindViewHolder is not called

RecyclerView在滚动上崩溃

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