Question

执行此方法时：

public static List<T> ToList<T>(DataTable dataTable)
        {
            Type type = typeof(T);

            List<T> list = new List<T>();

            foreach (DataRow dr in dataTable.Rows)
            {
                object[] args = new object[1];

                args[0] = dr;

                list.Add((T)Activator.CreateInstance(type, args));
            }

            return list;
        }

我得到了这个例外：

Constructor on type 'Northwind.BO.Products' not found.

但我知道我已经在Products类中声明了一个构造函数。

public class Products
{
    private int _ProductID;
    [DataMapping("ProductID", -99)]
    public int ProductID
    {
        get { return _ProductID; }
        set
        {
            if (_ProductID <= 0)
            {
                _ProductID = value;
            }
            else
            {
                throw new Exception("ID should not be set manually!");
            }
        }
    }

    private string _ProductName;
    [DataMapping("ProductName", "")]
    public string ProductName
    {
        get { return _ProductName; }
        set { _ProductName = value;}
    }

    private int _SupplierID;
    [DataMapping("SupplierID", -99)]
    public int SupplierID
    {
        get { return _SupplierID; }
        set { _SupplierID = value;}
    }

    private int _CategoryID;
    [DataMapping("CategoryID", -99)]
    public int CategoryID
    {
        get { return _CategoryID; }
        set { _CategoryID = value;}
    }

    private string _QuantityPerUnit;
    [DataMapping("QuantityPerUnit", "")]
    public string QuantityPerUnit
    {
        get { return _QuantityPerUnit; }
        set { _QuantityPerUnit = value;}
    }

    private decimal _UnitPrice;
    [DataMapping("UnitPrice", -99.99)]
    public decimal UnitPrice
    {
        get { return _UnitPrice; }
        set { _UnitPrice = value;}
    }

    private short _UnitsInStock;
    [DataMapping("UnitsInStock", -99)]
    public short UnitsInStock
    {
        get { return _UnitsInStock; }
        set { _UnitsInStock = value;}
    }

    private short _UnitsOnOrder;
    [DataMapping("UnitsOnOrder", -99)]
    public short UnitsOnOrder
    {
        get { return _UnitsOnOrder; }
        set { _UnitsOnOrder = value;}
    }

    private short _ReorderLevel;
    [DataMapping("ReorderLevel", -99)]
    public short ReorderLevel
    {
        get { return _ReorderLevel; }
        set { _ReorderLevel = value;}
    }

    private bool _Discontinued;
    [DataMapping("Discontinued", false)]
    public bool Discontinued
    {
        get { return _Discontinued; }
        set { _Discontinued = value;}
    }

public Products(object[] args)
{
}

public Products()
{
}

Answer 1

问题是Northwind.BO.Products类没有public构造函数，只需要一个DataRow。

你能告诉我们它有什么构造函数吗？

Answer 2

您不需要任何Northwind类的构造函数 - 根据例外，您需要Northwind.BO.Products上的正确的构造函数。

此外，正如Activator.CreateInstance所使用的，此构造函数必须具有与您传递给它的参数匹配的正确签名。由于您要向其传递参数，因此默认构造函数将不匹配。

当我读到你的问题时，它必须有这个构造函数

public Products(DataRow dr)

Answer 3

构造函数大多数签名可能与您提供的参数不匹配。

DataTable to List <t>转换问题</t>

3 个答案: