[英]C# and Base-to-Derived Class Casting
我想將信息從基類實例列表投影到派生類實例列表中,但是我一直在遇到強制轉換異常。 這是我要執行的操作的示例...如何使其起作用?
以下代碼位於http://ideone.com/CaXQS上 ,如果有幫助的話...謝謝!
using System;
using System.Collections.Generic;
namespace AddingReversedNumbers
{
public class MyDerivedClass : MyBaseClass, IMyInterface
{
public int InterfaceProperty { get; set; }
public int DerivedClassProperty { get; set; }
public List<int> DerivedClassList { get; set; }
}
public class MyBaseClass
{
public int BaseClassProperty { get; set; }
}
public interface IMyInterface
{
int InterfaceProperty { get; set; }
}
class Program
{
static void Main()
{
//// This code works just fine.
//var derivedList = new List<MyDerivedClass>();
//derivedList.Add(new MyDerivedClass { BaseClassProperty = 10, DerivedClassProperty = 20, InterfaceProperty = 30 });
//derivedList.Add(new MyDerivedClass { BaseClassProperty = 20, DerivedClassProperty = 40, InterfaceProperty = 60 });
//var baseList = derivedList.ConvertAll(x => (MyBaseClass)x);
// This code breaks when ConvertAll() is called.
var baseList = new List<MyBaseClass>();
baseList.Add(new MyBaseClass{ BaseClassProperty = 10 });
baseList.Add(new MyBaseClass{ BaseClassProperty = 20 });
var derivedList = baseList.ConvertAll(x => (MyDerivedClass)x);
}
}
}
在您的ConvertAll
代碼中,您只是強制轉換。 您不能將基類實例轉換為派生類實例。 例如,您希望將object
強制轉換為FileStream
做什么? 它指的是哪個文件?
如果要在ConvertAll
投影中創建一個新對象,只需執行以下操作:
var derivedList = baseList.ConvertAll
(x => new MyDerivedClass { BaseClassProperty = x.BaseClassProperty });
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