如何使用 Recycler View 的长按位置获取 SQLite 列值？

Question

我正在尝试通过长按该行从我的 SQLite 表中删除项目（最终将使用一个按钮，但现在只是长按测试）。但是我正在努力删除正确的。对于上下文，当我向表中添加新行时，它们会得到一个 ID 号。然后我想在长按时使用该 ID 号删除它们。我已经删除了一些下面不相关的代码。

MainActivity.java：

public class MainActivity extends AppCompatActivity implements StockViewInterface {

    private DBHandler db;
    private Stock stock;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        RecyclerView stockView = findViewById(R.id.rvStock);
        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
        stockView.setLayoutManager(linearLayoutManager);
        stockView.setHasFixedSize(true);
        db = new DBHandler(this);
        stock = new Stock();
        ArrayList<Stock> allStock = db.getAllStock();

        if (allStock.size() > 0) {
            stockView.setVisibility(View.VISIBLE);
            StockAdapter stockAdapter = new StockAdapter(this, allStock, this);
            stockView.setAdapter(stockAdapter);
        }
        else {
            stockView.setVisibility(View.GONE);
            Toast.makeText(this, "No Items!", Toast.LENGTH_LONG).show();
        }
    }

    @Override
    public void onLongItemClick(int position) {
        Toast.makeText(this, "long pressed", Toast.LENGTH_SHORT).show();
        db.deleteStockItem(db.getStockItem(stock.getID()));
    }
}

DBHandler.java：

public class DBHandler extends SQLiteOpenHelper {
    private static final int DATABASE_VERSION = 1;
    private static final String DATABASE_NAME = "ITStock";
    private static final String TABLE_STOCK = "stock";
    private static final String KEY_ID = "id";
    private static final String KEY_ITEM = "item";
    private static final String KEY_CONDITION = "condition";
    private static final String KEY_QUANTITY = "quantity";
    private static final String KEY_LOCATION = "location";
    private static final String KEY_CATEGORY = "category";

    public DBHandler(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    // Creating Table
    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_STOCK_TABLE = "CREATE TABLE " + TABLE_STOCK + "(" + KEY_ID
                + " INTEGER PRIMARY KEY,"
                + KEY_ITEM + " TEXT,"
                + KEY_CONDITION + " TEXT,"
                + KEY_QUANTITY + " INT,"
                + KEY_LOCATION + " TEXT,"
                + KEY_CATEGORY + " TEXT" + ")";
        db.execSQL(CREATE_STOCK_TABLE);
    }

    // Upgrading Database
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // Drop older table if existed
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_STOCK);
        // Create tables again
        onCreate(db);
    }

    // Get a single stock item
    Stock getStockItem(int id) {
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.query(TABLE_STOCK, new String[] { KEY_ID, KEY_ITEM, KEY_CONDITION, KEY_QUANTITY, KEY_LOCATION, KEY_CATEGORY}, KEY_ID + "=?",
                new String[] {String.valueOf(id)}, null, null, null, null);
        if (cursor != null)
            cursor.moveToFirst();
        Stock stock = new Stock(Integer.parseInt(cursor.getString(0)), cursor.getString(1), cursor.getString(2), cursor.getInt(3),
                cursor.getString(4), cursor.getString(5));
        return stock;
    }

    // Get all stock items
    public ArrayList<Stock> getAllStock() {
        String selectQuery = "SELECT * FROM " + TABLE_STOCK;
        SQLiteDatabase db = this.getWritableDatabase();
        ArrayList<Stock> stockList = new ArrayList<>();
        Cursor cursor = db.rawQuery(selectQuery, null);
        if (cursor.moveToFirst()) {
            do {
                int id = Integer.parseInt(cursor.getString(0));
                String item = cursor.getString(1);
                String condition = cursor.getString(2);
                int quantity = cursor.getInt(3);
                String location = cursor.getString(4);
                String category = cursor.getString(5);
                stockList.add(new Stock(id, item, condition, quantity, location, category));
            } while (cursor.moveToNext());
        }
        cursor.close();
        return stockList;
    }

    // Delete single stock item
    public void deleteStockItem(Stock stock) {
        SQLiteDatabase db = this.getWritableDatabase();
        db.delete(TABLE_STOCK, KEY_ID + " = ?", new String[] {String.valueOf(stock.getID())});
        db.close();
    }
}

Stock.java：

public class Stock {
    int id;
    String item;
    String condition;
    int quantity;
    String location;
    String category;

    public Stock(){ }
    public Stock(int id, String item, String condition, int quantity, String location, String category) {
        this.id = id;
        this.item = item;
        this.condition = condition;
        this.quantity = quantity;
        this.location = location;
        this.category = category;
    }

    public Stock(String item, String condition, int quantity, String location, String category) {
        this.item = item;
        this.condition = condition;
        this.quantity = quantity;
        this.location = location;
        this.category = category;
    }

    // Getters and setters
    public int getID() {
        return this.id;
    }

    public void setID(int id) {
        this.id = id;
    }

    public String getItem() {
        return this.item;
    }

    public void setItem(String item) {
        this.item = item;
    }

    public String getCondition() {
        return this.condition;
    }

    public void setCondition(String condition) {
        this.condition = condition;
    }

    public int getQuantity() {
        return this.quantity;
    }

    public void setQuantity(int quantity) {
        this.quantity = quantity;
    }

    public String getLocation() {
        return this.location;
    }

    public void setLocation(String location) {
        this.location = location;
    }

    public String getCategory() {
        return this.category;
    }

    public void setCategory(String category) {
        this.category = category;
    }
}

StockAdapter.java：

public class StockAdapter extends RecyclerView.Adapter<StockAdapter.ViewHolder> {

    private Context context;
    private ArrayList<Stock> listStock;
    private ArrayList<Stock> mArrayList;
    private DBHandler db;
    private MainActivity mainActivity;
    private StockViewInterface stockViewInterface;

    StockAdapter(Context context, ArrayList<Stock> listStock, StockViewInterface stockViewInterface) {
        this.context = context;
        this.listStock = listStock;
        this.mArrayList = listStock;
        this.stockViewInterface = stockViewInterface;
        db = new DBHandler(context);
        mainActivity = new MainActivity();
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        LayoutInflater inflater = LayoutInflater.from(parent.getContext());
        View stockView = inflater.inflate(R.layout.stock_row, parent, false);
        return new ViewHolder(stockView);
    }

    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        final Stock stock = listStock.get(position);
        holder.tvItem.setText(stock.getItem());
        holder.tvCondition.setText(stock.getCondition());
        holder.tvQuantity.setText(String.valueOf(stock.getQuantity()));
        holder.tvLocation.setText(stock.getLocation());
        holder.tvCategory.setText(stock.getCategory());
    }

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

    class ViewHolder extends RecyclerView.ViewHolder {
        final TextView tvItem;
        final TextView tvCondition;
        final TextView tvQuantity;
        final TextView tvLocation;
        final TextView tvCategory;
        View stockView;

        ViewHolder(View stockView) {
            super(stockView);
            this.stockView = stockView;
            stockView.setOnClickListener(v -> stockViewInterface.onItemClick(getAdapterPosition()));
            stockView.setOnLongClickListener(v -> {
                stockViewInterface.onLongItemClick(getAdapterPosition());
                return false;
            });
            tvItem = stockView.findViewById(R.id.tvItem);
            tvCondition = stockView.findViewById(R.id.tvCondition);
            tvQuantity = stockView.findViewById(R.id.tvQuantity);
            tvLocation = stockView.findViewById(R.id.tvLocation);
            tvCategory = stockView.findViewById(R.id.tvCategory);
        }
    }
}

我的 deleteStockItem 方法正在 MainActivity 中使用以下内容（1 是 ID 号）：

db.deleteStockItem(db.getStockItem(1))

我不想手动输入 ID 号，所以它需要类似于

db.deleteStockItem(db.getStockItem(getID))

但我不知道该怎么做。 我试过这样做：

db.deleteStockItem(db.getStockItem(stock.getID()));

并得到这个错误：

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.it_stock, PID: 14325
    android.database.CursorIndexOutOfBoundsException: Index 0 requested, with a size of 0
        at android.database.AbstractCursor.checkPosition(AbstractCursor.java:460)
        at android.database.AbstractWindowedCursor.checkPosition(AbstractWindowedCursor.java:136)
        at android.database.AbstractWindowedCursor.getString(AbstractWindowedCursor.java:50)
        at com.example.it_stock.DBHandler.getStockItem(DBHandler.java:71)
        at com.example.it_stock.MainActivity.onLongItemClick(MainActivity.java:74)
        at com.example.it_stock.StockAdapter$ViewHolder.lambda$new$1$StockAdapter$ViewHolder(StockAdapter.java:71)
        at com.example.it_stock.-$$Lambda$StockAdapter$ViewHolder$glwJYV6g13zGeNPhabWeayxaKNY.onLongClick(lambda)
        at android.view.View.performLongClickInternal(View.java:5714)
        at android.view.View.performLongClick(View.java:5672)
        at android.view.View.performLongClick(View.java:5690)
        at android.view.View$CheckForLongPress.run(View.java:22402)
        at android.os.Handler.handleCallback(Handler.java:751)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:154)
        at android.app.ActivityThread.main(ActivityThread.java:6121)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:889)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:779)

Answer 1

我认为这是因为您的 stock 对象中没有任何项目。

我检查了你的代码，你应该更新它

• 您应该在onBindViewHolder 函数中编写setOnLongClickListener 事件并将其从ViewHolder 函数中删除。

您的onBindViewHolder 将是这样的：

@Override
public void onBindViewHolder(ViewHolder holder, int position) {
    final Stock stock = listStock.get(position);
    holder.tvItem.setText(stock.getItem());
    holder.tvCondition.setText(stock.getCondition());
    holder.tvQuantity.setText(String.valueOf(stock.getQuantity()));
    holder.tvLocation.setText(stock.getLocation());
    holder.tvCategory.setText(stock.getCategory());


    stockView.setOnLongClickListener(v -> {
            stockViewInterface.onLongItemClick(position);
            return false;
        });

}

• 您的MainActivity.java 有一些变化：

public class MainActivity extends AppCompatActivity implements StockViewInterface {

    private DBHandler db;

    // remove this you don't need it
    //private Stock stock;

    // set allStock global to be easy to use
    private ArrayList<Stock> allStock = new ArrayList<Stock>();

    // set your adapter here
    private  StockAdapter stockAdapter ;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        RecyclerView stockView = findViewById(R.id.rvStock);
        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
        stockView.setLayoutManager(linearLayoutManager);
        stockView.setHasFixedSize(true);
        db = new DBHandler(this);

        // remove this you don't need it
        //stock = new Stock();

        // here you can get list from db
        allStock = db.getAllStock();

        if (allStock.size() > 0) {
            stockView.setVisibility(View.VISIBLE);

            stockAdapter = new StockAdapter(this, allStock, this);
            stockView.setAdapter(stockAdapter);
        }
        else {
            stockView.setVisibility(View.GONE);
            Toast.makeText(this, "No Items!", Toast.LENGTH_LONG).show();
        }
    }

    @Override
    public void onLongItemClick(int position) {
        Toast.makeText(this, "long pressed", Toast.LENGTH_SHORT).show();
        // here you get id of the item you need to delete it
        db.deleteStockItem(db.getStockItem(allStock.get(position).getID()));

        // now you can delete the same item from your model
        allStock.remove(position);

        // update your view here
        stockAdapter.notifyItemRemoved(position);
    }
}

Answer 2

如果我正确理解了您的问题，我认为这种方法 在 MainActivity 中对你有用。

@Override
public void onLongItemClick(int position) {
    Toast.makeText(this, "long pressed", Toast.LENGTH_SHORT).show();
    StockItem si = (StockItem) getItemAtPosition(position);
    db.deleteStockItem(si.getId);
}