C# 在c中强制转换泛型类型

我有一个如下的结构。我很难返回一个通用集合。我错过了什么

class Program
{
    static void Main()
    {
          BusinessCollection businessCollection = new BusinessCollection();

          //Why this is not working because businesscollection is a GenericCollection<BusinessEntity>
          businessCollection = new GenericCollection<BusinessEntity>();

          //or neither this
         businessCollection = (BusinessCollection)new GenericCollection<BusinessEntity>();
    }
}



public class BusinessEntity
{
   public string Foo { get; set;}
}

public class BusinessCollection : GenericCollection<BusinessEntity>
{
     //some implementation here
}

public class GenericCollection<T> : ICollection<T>
{
    //some implementation here
}

---

检查您的假设：

businesscollection是一个通用集合

---

是的，但您将其声明为Businesscollection类型。并非所有GenericCollection都是BusinessCollection，但这正是您试图分配给BusinessCollection的内容。

您无法执行您想要执行的操作。反之亦然

class Program
{
    static void Main()
    {
          GenericCollection<BusinessEntity> businessCollection = new BusinessCollection();
          //this will work
          BusinessCollection tempCollection = (BusinessCollection)businessCollection ;
    }
}



public class BusinessEntity
{
   public string Foo { get; set;}
}

public class BusinessCollection : GenericCollection<BusinessEntity>
{
     //some implementation here
}

public class GenericCollection<T> : ICollection<T>
{
    //some implementation here
}

所有BusinessCollection实际上都是GenericCollection，但您不能确定所有GenericCollection都是BusinessCollection的

因此，以下方法将起作用

class Program
{
    static void Main()
    {
          GenericCollection<BusinessEntity> businessCollection = new BusinessCollection();
          //this will work
          BusinessCollection tempCollection = (BusinessCollection)businessCollection ;
    }
}



public class BusinessEntity
{
   public string Foo { get; set;}
}

public class BusinessCollection : GenericCollection<BusinessEntity>
{
     //some implementation here
}

public class GenericCollection<T> : ICollection<T>
{
    //some implementation here
}

---

因为正方形是矩形，但并非所有的矩形都是正方形。在本例中，BusinessCollection是GenericCollection，但并非所有GenericCollection对象都是BusinessCollection对象。类型为BusinessCollection的变量可以指向GenericCollection对象，但不能指向其他对象。

businessCollections类型为BusinessCollection；只能为其分配属于BusinessCollection的内容。但是，GenericCollection不是BusinessCollection。就像动物不是狗而是狗一样

这可以在运行时或编译时进行验证。运行时选项是您的强制转换：

businessCollection = (BusinessCollection){some expression};

这是使用“动物可能是狗”测试，即检查我们正在考虑的特定动物是否真的是狗。它将此检查推迟到运行时。这就是为什么这行代码可以编译，但实际上没有运行。特定的动物从来不是真正的狗