java - Android Studio从回收者 View 和列表中删除项目

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What is a NullPointerException, and how do I fix it?

（12个答案）


3个月前关闭。





当我单击特定项目时，我试图将其删除。我已经运行了日志，所以我知道它正在选择一个项目，我只是不明白错误的含义。如果重要的话，我正在使用会议室数据库并使用回收站视图。


java.lang.NullPointerException：尝试调用虚拟方法'void
uk.edu.le.co2103.myrecipebook.RecipeListAdapter.notifyItemRemoved（int）'在空对象上
参考
在uk.edu.le.co2103.myrecipebook.MainActivity $ 4.onClick（MainActivity.java:126）


我检查了清单中是否有数据，因此下面是日志。


D /主要活动：列表：[uk.edu.le.co2103.myrecipebook.Recipe@c97e34d，uk.edu.le.co2103.myrecipebook.Recipe@e7b6e02，uk.edu.le.co2103.myrecipebook.Recipe@d9ea313]
2020-04-01 23：07：29.300 25679-25679 / uk.edu.le.co2103.myrecipebook D / MAIN活动：索引：2


这是主要活动中我删除部分的代码

    public void onItemClick(int position, View view) {
        Log.d(TAG, "onItemClick Position: " + position);
    AlertDialog.Builder alertDialog = new AlertDialog.Builder(this);
    alertDialog.setTitle("Edit or Delete...");
    alertDialog.setPositiveButton("Edit", new
 DialogInterface.OnClickListener()
 alertDialog.setNegativeButton("Delete", new
 DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialogInterface, int i) {
            //Delete
            Log.d(TAG, "List: " + recipesList);
            Log.d(TAG, "Index: " + position);
            int removeIndex = position;
            recipesList.remove(removeIndex);
            mAdapter.notifyItemRemoved(removeIndex);


        }
    });

我的适配器代码

 public class RecipeListAdapter extends
 RecyclerView.Adapter<RecipeListAdapter.RecipeViewHolder> {
private OnItemClickListener mListener;
private LiveData<List<Recipe>> recipeList;


public interface OnItemClickListener{
    void onItemClick(int position, View view);

}
public void setOnItemClickListener(OnItemClickListener listener){
    mListener = listener;
}




class RecipeViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
    private final TextView recipeItemView;

    private RecipeViewHolder(View itemView) {
        super(itemView);
        recipeItemView = itemView.findViewById(R.id.textView);
        itemView.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v){
                if (mListener != null){
                    int position = getAdapterPosition();
                    if (position != RecyclerView.NO_POSITION){
                        mListener.onItemClick(position, v);
                    }
                }
            }
        });
    }

    @Override
    public void onClick(View view) {
        mListener.onItemClick(getAdapterPosition(), view);
    }
}

private final LayoutInflater mInflater;
private List<Recipe> mRecipes; // Cached copy of words

RecipeListAdapter(Context context) {
    mInflater = LayoutInflater.from(context);
    this.recipeList = recipeList;
}

@Override
public RecipeViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View itemView = mInflater.inflate(R.layout.recyclerview_item, parent, false);
    return new RecipeViewHolder(itemView);
}

@Override
public void onBindViewHolder(RecipeViewHolder holder, int position) {
    if (mRecipes != null) {
        Recipe current = mRecipes.get(position);
        holder.recipeItemView.setText(current.getName());
    } else {
        // Covers the case of data not being ready yet.
        holder.recipeItemView.setText("No Recipes");
    }
}

void setWords(List<Recipe> recipes){
    mRecipes = recipes;
    notifyDataSetChanged();
}


// getItemCount() is called many times, and when it is first called,
// mWords has not been updated (means initially, it's null, and we can't return null).
@Override
public int getItemCount() {
    if (mRecipes != null)
        return mRecipes.size();
    else return 0;
}
public interface OnNoteListener{}

}

最佳答案

您可以在这里共享您的适配器代码吗？过去我遇到过这个问题，它的发生是因为您需要刷新适配器中的列表内容（您现在仅通过.notifyItemRemoved（int index）注意到它），但我确实需要查看您的适配器以帮助您了解如何做到这一点，在我看来，观察员是最好的方法。