从SQLITE数据库获取时，我的listadapter中没有数据

Question

我是Android编程的新手，我想为产品创建数据库。我按照教程，但仍然有一些错误，但我修复了它们，但这是我迄今为止最大的问题。当我输入数据时，它只是说＆＃34;数据添加成功！＆＃34;但我的列表适配器中没有任何内容。

这是我的databaseHandler

    private static final  String prodID = "ID ";
    private static final String PRODNAME = "ProdName";
    private static final String CATEGORY = "Category";

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

    }


    @Override
    public void onCreate(SQLiteDatabase db) {
        String createTable  = "create table " + TABLE_NAME + " ( " + prodID + " String primary key," + PRODNAME + " text not null,"
                + CATEGORY + " text not null);";
        db.execSQL(createTable);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
        onCreate(db);
    }



    public  boolean NewData (String PROD_ID, String prodNAME,String Category) {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(prodID, PROD_ID);
        values.put(PRODNAME, prodNAME);
        values.put(CATEGORY, Category);


        long result = db.insert(TABLE_NAME, null, values);

        if (result == -1) {
            return false;
        } else {
            return true;
        }
    }
    public Cursor getListContents() {
        SQLiteDatabase db = this.getWritableDatabase();
        return db.rawQuery("SELECT * FROM " + TABLE_NAME, null);
   }

我想要添加新数据

    prodID = findViewById(R.id.editText5);
        PROD_NAME =  findViewById(R.id.editText4);
        CATEGORY =  findViewById(R.id.editText3);

        btnAdd =  findViewById(R.id.btnAdd) ;
        db = new DatabaseHANDLER(this);

        Button btnAdd = findViewById(R.id.btnAdd);
        btnAdd.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String product_ID = prodID.getText().toString();
                String prod_name = PROD_NAME.getText().toString();
                String category = CATEGORY.getText().toString();


                if(prod_name.length() != 0 && product_ID.length() != 0 && category.length() != 0){

                    NewData(product_ID,prod_name, category);
                    prodID.setText(" ");
                    PROD_NAME.setText(" ");
                    CATEGORY.setText(" ");



                }
                else {
                    Toast.makeText(NewData.this, "Fill the forms completely!",Toast.LENGTH_LONG)
                            .show();
                }

            }
        });


    }
    public void NewData(String PROD_ID, String prodNAME,String CATEGORY){
        boolean insertData = db.NewData(PROD_ID, prodNAME, CATEGORY);
        if(insertData == true) {
            Toast.makeText(NewData.this, "Data inserted Successfully!", Toast.LENGTH_LONG).show();
        }
        else {
            Toast.makeText(NewData.this,"Too bad, something went wrong :( ", Toast.LENGTH_LONG).show();
        }
    }

}

这是我的列表适配器

private LayoutInflater mInflater;
private ArrayList<Products> products;
private int mViewResourceId;

public ThreeColumn_ListAdapter(Context context, int textViewResourceId, ArrayList<Products> products) {
    super(context, textViewResourceId, products);
    this.products = products;
    mInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    mViewResourceId = textViewResourceId;
    Products products1;
}

public View getView(int position, View convertView, ViewGroup parent) {
    convertView = mInflater.inflate(R.layout.view_data,parent,false);

    Products products1 = products.get(position);

    if (products != null) {
        TextView ProdID = (TextView) convertView.findViewById(R.id.textProdID);
        TextView ProdName = (TextView) convertView.findViewById(R.id.textProdName);
        TextView Category = (TextView) convertView.findViewById(R.id.textCategory);
        if (ProdID != null) {
            ProdID.setText(products1.getProdID());
        }
        if (ProdName != null) {
            ProdName.setText(products1.getProdNAME());
        }
        if (Category != null) {
            Category.setText((products1.getCategory()));
        }

    }

    return convertView;
} 

这是我的视图数据类

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.view_data);
    databaseHANDLER = new DatabaseHANDLER(this);
    ProductList = new ArrayList<>();
    Cursor data = databaseHANDLER.getListContents();

    int numrows = data.getCount();
    if (data.getCount() == 0){
        Toast.makeText(viewdata.this, "There is nothing in this database!",Toast.LENGTH_LONG).show();
    }
    else{

        int i = 0;
        while (data.moveToNext()){
            products = new Products(data.getString(0),data.getString(1),data.getString(2));
            ProductList.add(i,products);
        }
        ListAdapter adapter = new ArrayAdapter<>(this, R.layout.view_data,ProductList);
        listView = (ListView) findViewById(R.id.list_view);
        listView.setAdapter(adapter);
    }

}

感谢您的帮助：）