Question

我有一些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网格。当我在网格中移动时，发生了两件事

选择第二个位置的项目。例如，我在位置0并且想要选择位置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。

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;
}

滚动侦听器

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

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

更改此类代码并尝试。

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));
    }

崩溃的原因。

Answer 2

当我在滚动期间使用自定义翻译开发库时，我遇到了同样的问题。只有在快速滚动时，当我尝试从List访问View元素时，这是null，这里是NPE。

所以有一个非常简单的解决方案只是跳过元素，这是空的，并继续新的元素。就我而言，它是这样的：

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

这种情况发生在ScrollView（它是RecycleView，ListView等的父级）的基础上。当我们尝试访问正在重绘的View时。无论如何只需简单的Null检查就可以解决您的问题。

更新1：

同样基于缓存查看RecyclerView的布局，您还需要另一个选项。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

RecyclerView在滚动

3 个答案: