RecyclerView 在滚动时崩溃

Question

我有一些以水平网格排列的图像。我想使用键事件从左到右和从右到左移动我的网格。当我穿过网格时发生了两件事

1. 第二个位置的项目被选中。例如，我在位置 0 并想选择位置 1 的下一项，但我的网格选择位置 2 的项并跳过位置 1 的项。

2. 滚动时出现空指针异常

   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;
   }
   

滚动监听器

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());
           }

        }

这是我的日志

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

在代码中gridHolder.itemView.setSelected(true); gridHolder 为空。

这样改代码试试。

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));
    }

崩溃的原因。

Answer 2

当我在滚动期间开发带有自定义翻译的库时，我遇到了同样的问题。仅在快速滚动中，当我尝试从 List 访问 View 元素时，它为空，这里是 NPE。

所以有一个非常简单的解决方案，只是跳过元素，它是空的，然后继续新的。在我的情况下是这样的：

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

当我们尝试访问正在重绘的 View 时，基于 ScrollView（它是 RecycleView、ListView 等的父级）会发生这种情况。无论如何，只需简单的 Null 检查即可解决您的问题。

更新 1：

同样基于 RecyclerView 的缓存视图布局，你需要另一种选择。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);
            }
        }
}

Answer 3

根据错误很明显

(GridView_Holder)mRecyclerView.findViewHolderForPosition(mCurrentSelectedPosition);

为空。这就是崩溃的原因。

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