如何修复 Recyclerview 项目删除显示错误

Question

我有一个回收站视图。 recyclerview中有城市名称，当我长按时，我想从recyclerview中删除它。我在适配器类中写了一些代码。当我点击城市名称时，我可以删除它们，但是当我再次查看recyclerview时，我删除的城市名称又出现了。我该如何解决这个问题？

我的适配器类

public class Adapter extends RecyclerView.Adapter<Adapter.MyViewHolder>  {

ArrayList<City> arrayList;
Context context;

public Adapter(ArrayList<City> arrayList ,Context context ){
    this.arrayList = arrayList;
    this.context = context;

}

@NonNull
@Override
public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {

    RecyclerviewRowBinding recyclerviewRowBinding = RecyclerviewRowBinding.inflate(LayoutInflater.from(parent.getContext()),parent,false);
    return new MyViewHolder(recyclerviewRowBinding);

}

@Override
public void onBindViewHolder(@NonNull Adapter.MyViewHolder holder, int position) {

    holder.binding.MytxtCities.setText(arrayList.get(position).cityName);


    holder.itemView.setOnLongClickListener(new View.OnLongClickListener() {
        @Override
        public boolean onLongClick(View v) {
            AlertDialog.Builder builder = new AlertDialog.Builder(context);
            builder.setIcon(R.drawable.warningicon);
            builder.setMessage("Are you sure that you want to delete "+arrayList.get(position).cityName);
            builder.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    arrayList.remove(position);
                    notifyItemRemoved(position);
                    notifyItemRangeChanged(position,arrayList.size());
                }
            }).setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {

                }
            }).show();

            return true;
        }
    });


    holder.itemView.setOnClickListener(v -> {
        Intent intent = new Intent(holder.itemView.getContext(),MainActivity.class);
        intent.putExtra("citId",arrayList.get(position).id);
        holder.itemView.getContext().startActivity(intent);
    });
}

@Override
public int getItemCount() {
    return arrayList.size();
}



public class MyViewHolder extends RecyclerView.ViewHolder {
    TextView Mytxt_cities;
    private RecyclerviewRowBinding binding;

    public MyViewHolder(@NonNull RecyclerviewRowBinding binding) {
        super(binding.getRoot());
        this.binding = binding;
        Mytxt_cities = itemView.findViewById(R.id.Mytxt_cities);



    }


}

}

我的 recyclerview 类是城市类

public class cities extends AppCompatActivity {

RecyclerView recyclerView ;
ArrayList<City> cityArrayList;
Adapter cityadapter;
ImageView cities_back_icon;



public void init(){

    cities_back_icon = findViewById(R.id.Id_cities_back_icon);
    cities_back_icon_click_register();

    cityArrayList = new ArrayList<>();
    recyclerView = findViewById(R.id.recyclerview_id);



    SQLGet_Data();

}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_cities);
    init();


}

private void cities_back_icon_click_register(){

    cities_back_icon.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(cities.this, MainActivity.class);
            startActivity(intent);
        }
    });
}

private void SQLGet_Data(){
    try {

        SQLiteDatabase sqLiteDatabase = this.openOrCreateDatabase("City",MODE_PRIVATE,null);
        Cursor cursor = sqLiteDatabase.rawQuery("SELECT*FROM city",null);
        int idIx = cursor.getColumnIndex("id");
        int nameIx = cursor.getColumnIndex("cityname");

        while(cursor.moveToNext()){
            String cityname = cursor.getString(nameIx);
            int id = cursor.getInt(idIx);
            City city = new City(cityname,id);
            cityArrayList.add(city);
        }
        cityadapter.notifyDataSetChanged();
        cursor.close();
    }

    catch (Exception e ){
       e.printStackTrace();
    }
                 /*---------------------- set recyclerview-----------------------------*/

    recyclerView.setLayoutManager(new LinearLayoutManager(cities.this));
    cityadapter = new Adapter(cityArrayList,this);
    recyclerView.setAdapter(cityadapter);





/*--------------------------We drew a line between the data in the recyclerview------------------------------------*/

    DividerItemDecoration dividerItemDecoration = new DividerItemDecoration(recyclerView.getContext(), DividerItemDecoration.VERTICAL);
    Drawable drawable = ContextCompat.getDrawable(getApplicationContext(), R.drawable.custom_divider);
    dividerItemDecoration.setDrawable(drawable);
    recyclerView.addItemDecoration(dividerItemDecoration);

}

}

Answer 1

问题是您只是从适配器内的ArrayList 中删除城市。但是这些城市仍然保留在您的 SQL 数据库中。然后，当您重新启动 Activity 时，您的 ArrayList 将使用您的 SQL 数据库的数据创建，这些已删除的城市仍然存在。

要始终删除城市，您不仅需要删除适配器中的城市，还需要删除 SQL 数据库中的城市。