Android Studio从回收器视图和列表中删除项目

Question

当我点击某个特定项目时，我正试图删除它。我运行了日志，所以我知道它在挑选一个项目，但我不明白错误的含义。如果这很重要的话，我正在使用房间数据库和回收器视图。

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

我已经检查了列表中是否有数据，因此查看了下面的日志。

D/MAIN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.e.co2103.myrecipebook D/MAIN活动：索引：2

这是我删除主活动部分的代码

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{}

}

Answer 1

你能在这里分享你的适配器代码吗？我以前遇到过这个问题，之所以会出现这个问题，是因为你需要刷新适配器中的列表内容(你现在只注意到了.notifyItemRemoved(int index((，但我确实需要查看你的适配器来帮助你如何做到这一点，在我的情况下，观察者是最好的方法。

Answer 2

我认为您没有初始化适配器或列表。