Question

我已将此代码与json对象一起使用。现在我正在使用sqlite，并且它具有NPE错误。

    Cursor newRes = myDb.getAllData();
    while (newRes.moveToNext()) {
        Product product = new Product(Integer.parseInt(newRes.getString(0).toString()), Integer.parseInt(newRes.getString(1).toString()), newRes.getString(2).toString(),
                newRes.getString(3).toString(), newRes.getString(4).toString(), newRes.getString(5).toString(), Double.parseDouble(newRes.getString(6).toString()), newRes.getString(7).toString());
        productTransList.add(product);
    }

    adapter = new ProductAdapter(mCtx, productTransList);
    transRecyclerView.setAdapter(adapter);

编辑

07-13 09:05:29.763 13314-13351/com.example.arlene.capsmobile E/libdataflow_monitor: open error=Operation not permitted
07-13 09:05:31.542 13314-13314/com.example.arlene.capsmobile E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.arlene.capsmobile, PID: 13314
java.lang.NullPointerException: Attempt to invoke interface method 'boolean java.util.List.add(java.lang.Object)' on a null object reference
    at com.example.arlene.capsmobile.translistTab.loadTransList(translistTab.java:135)
    at com.example.arlene.capsmobile.translistTab.onCreate(translistTab.java:72)

错误productTransList.add(product);

Answer 1

首先初始化productTransList，然后将对象添加到列表中。

productTransList = new ArrayList<>();

这将解决问题。

Answer 2

在您的SQLiteHelper类中，您需要初始化列表：

public List<Product> getAllProducts() {
    try {
        List<Product > listProducts = new ArrayList<>();
        String selectQuery = "SELECT * FROM " + dbSchema.table_name;
        SQLiteDatabase mDb = this.getWritableDatabase();
        Cursor cursor = mDb.rawQuery(selectQuery, null);

        if (cursor.moveToFirst()) {
            do {
                Product product = new 
                Product(Integer.parseInt(cursor.getString(0).toString()), 
                Integer.parseInt(cursor.getString(1).toString()), 
                cursor.getString(2).toString(),
                cursor.getString(3).toString(), 
                cursor.getString(4).toString(), 
                cursor.getString(5).toString(), 
                Double.parseDouble(cursor.getString(6).toString()), 
                cursor.getString(7).toString());
                listProducts.add(mRecord);
            } while (cursor.moveToNext());
        }
        return listProducts;
    } catch (Exception ex) {
        return null;
    }
}

这里是SQLite的参考： SQLite Demo

在您的活动中，异步使用辅助方法getAllProducts并将空列表作为输入参数传递给它。

Answer 3

首先初始化ArrayList

 productTransList = new ArrayList<>();
 Cursor newRes = myDb.getAllData();
    while (newRes.moveToNext()) {
        Product product = new Product(Integer.parseInt(newRes.getString(0).toString()), Integer.parseInt(newRes.getString(1).toString()), newRes.getString(2).toString(),
                newRes.getString(3).toString(), newRes.getString(4).toString(), newRes.getString(5).toString(), Double.parseDouble(newRes.getString(6).toString()), newRes.getString(7).toString());
        productTransList.add(product);
    }

    adapter = new ProductAdapter(mCtx, productTransList);
    transRecyclerView.setAdapter(adapter);

希望这可能对您有帮助

从sqlite获取数据到回收站视图

3 个答案: