RecyclerView在滾動上崩潰

Question

我有一些圖像排列在水平網格中。我想使用關鍵事件從左到右和從右到左移動我的網格。當我通過網格移動時，發生了兩件事

1. 選擇了第二個位置的項目。例如，我處於位置0並想要選擇位置1處的下一個項目，但我的網格選擇位置2項目並跳過位置1項目。

2. 上滾動我得到空指針異常

   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; 
   } 
   

滾動收聽

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()); 
      } 

     } 

這是我的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) 

Answer 1

當我在滾動期間開發了定製翻譯庫我有同樣的問題。只有在快速滾動時，當我試圖從列表中訪問視圖元素時，這是空的，這裏是NPE。

所以有一個非常簡單的解決方法，就是跳過空的元素，然後繼續添加新的元素。在我的情況是這樣的：

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

出現這種情況的基礎上，滾動型（這是RecycleView，ListView控件，等父母）當我們試圖訪問查看現在正在重繪。無論如何，只是簡單的空檢查應該可以解決你的問題。

更新1：

還可根據RecyclerView緩存視圖佈局，則需要另一種選擇。見下文。

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); 
      } 
     } 
} 

Answer 2

在代碼GR idHolder.itemView.setSelected（真）; gridHolder爲null。

更改這樣的代碼並嘗試。

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)); 
    } 

墜機原因。

Answer 3

按該錯誤很明顯，

(GridView_Holder)mRecyclerView.findViewHolderForPosition(mCurrentSelectedPosition); 

爲空。這是造成這次事故的原因。

您可以參考以下鏈接

FindViewHolderForPosition return null when card's not in vision

RecyclerView - findViewHolderForPosition always returns null when onBindViewHolder is not called