Android Studio Recycler视图删除项

Question

我正在尝试从回收者视图中删除项目。每次我在“回收商”视图中单击某个项目时，都会向我显示此错误。

java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'void uk.edu.le.co2103.myrecipebook.RecipeListAdapter.removeItem（int，java.util.List）'

我已确保我的列表已初始化，并使用日志来确保位置和列表中都包含值。

列表：[uk.edu.le.co2103.myrecipebook.Recipe @ f4d5298，uk.edu.le.co2103.myrecipebook.Recipe @ ca6aaf1]D /主要活动：索引：0

这是我的主要活动代码

public class MainActivity extends AppCompatActivity implements 
RecipeListAdapter.OnItemClickListener  {
private static final String TAG = "MAIN ACTIVITY";
private static final int RESULT_UPDATED = 300;
private RecipeViewModel mRecipeViewModel;
    public static final int NEW_WORD_ACTIVITY_REQUEST_CODE = 1;
    public String Name;
    public String Ingredients;
    public String Method;
    private RecipeListAdapter mAdapter;
    private RecipeDao recDao;
    Menu menu;
List<Recipe> recipesList = new ArrayList<>();

ListView search_items;

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);
        RecyclerView recyclerView = findViewById(R.id.recyclerview);
        RecipeListAdapter mAdapter = new RecipeListAdapter(this);
        recyclerView.setAdapter(mAdapter);
        mAdapter.setOnItemClickListener(MainActivity.this);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        mRecipeViewModel = new ViewModelProvider(this).get(RecipeViewModel.class);

        Log.d(TAG, "SIZE OF LIST: "+ recipesList);
        mRecipeViewModel.getAllRecipes().observe(this, new Observer<List<Recipe>>() {
            @Override
            public void onChanged(@Nullable final List<Recipe> recipes) {
                // Update the cached copy of the words in the adapter.
                int size = mAdapter.getItemCount();
                Log.d(TAG, "List of List : " + recipes);
                recipesList= recipes;
                mAdapter.setWords(recipes);
            }
        });

        FloatingActionButton fab = findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(MainActivity.this, AddRecipeActivity.class);
                startActivityForResult(intent, NEW_WORD_ACTIVITY_REQUEST_CODE);
            }
        });



}
public void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (requestCode == NEW_WORD_ACTIVITY_REQUEST_CODE && resultCode == RESULT_OK) {
        ArrayList<String> rData = data.getStringArrayListExtra(AddRecipeActivity.EXTRA_REPLY);
        String name = rData.get(0);
        String ingredients = rData.get(1);
        String method = rData.get(2);
        Recipe recipe = new Recipe(name, ingredients, method);
        RecipeViewModel.insert(recipe);
    }
   else {
        Toast.makeText(
                getApplicationContext(),
                R.string.empty_not_saved,
                Toast.LENGTH_LONG).show();
    }
}

@Override
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() {
        @Override
        public void onClick(DialogInterface dialogInterface, int i) {
            recipesList.get(position); //clicked item
            Intent update = new Intent(MainActivity.this, UpdateRecipeActivity.class);
            update.putExtra("Name", recipesList.get(position).getName()); //
            update.putExtra("Ingredients", recipesList.get(position).getIngredients());
            update.putExtra("Method", recipesList.get(position).getMethod());
            startActivity(update);

        }

    });
    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);


        }
    });
    alertDialog.setNeutralButton("Cancel", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialogInterface, int i) {

        }
    });
    alertDialog.show();
}

这是我的适配器代码

public class RecipeListAdapter extends 
RecyclerView.Adapter<RecipeListAdapter.RecipeViewHolder> {
private static final String TAG = "ADAPTER";
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

您可以使用它

public void deleteItem(final int position) {

 recipeList.remove(position);
 notifyDataSetChanged();

}

我希望它能与您合作