RecyclerView 在滚动时崩溃

Question

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。当我穿过网格时发生了两件事

第二个位置的项目已 selected。例如，我在位置 0 并想 select 位置 1 的下一个项目，但我的网格 select 位置 2 项目并跳过位置 1 项目。

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$ViewHolder.itemView' on a null object reference
at com.winettv.recylcerviewwithdpad.GridView_Recycler_Adapter.onKey(GridView_Recycler_Adapter.java:193)
at android.view.View.dispatchKeyEvent(View.java:9230)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1635)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1640)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1640)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1640)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1640)
at android.widget.ScrollView.dispatchKeyEvent(ScrollView.java:379)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1640)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1640)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1640)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1640)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1640)
at com.android.internal.policy.PhoneWindow$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

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

像这样更改代码并尝试。

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

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

Answer 3

当我在滚动过程中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，它才为 null，这里是 NPE。

所以有一个非常简单的解决方案，就是跳过空的元素，然后继续新的元素。在我的例子中是这样的：

// 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，只需简单的空检查就可以解决您的问题。

更新 1：

同样基于RecyclerView的缓存视图布局，你需要另一个选择。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);
            }
        }
}

RecyclerView 在滚动时崩溃

RecyclerView crashes on scrolling

java

android

android-recyclerview

scroller

key-events