[英]Creating a collection of base class, then access properties of derived classes in the collection items
我有这样的课程
class Base
{
int Id { get; set; }
}
class Derived1 : Base
{
string DerivedProperty1 { get; set; }
}
class Derived2 : Base
{
string DerivedProperty2 { get; set; }
}
现在我有一个这样的收藏课
public class MyCollection
{
List<Base> items;
public void Add(Base baseItem)
{
// if baseItem is Derived1, if items contain an item of type Derived1 and has the same DerivedProperty1 value as baseItem, throw exception
// if baseItem is Derived2, if items contain an item of type Derived2 and has the same DerivedProperty2 value as baseItem, throw exception
items.Add(baseItem);
}
}
我认为先检查baseItem的类型然后进行转换不是一种很好的做法,对吗? 否则,您如何建议我解决此设计问题?
根据您的代码和注释,正确的方法是为Base
提供IsDuplicateOf
方法,并在派生类中重写此方法。 像这样:
class Base
{
int Id { get; set; }
public virtual bool IsDuplicateOf(Base other)
{
return other != null && Id == other.Id;
}
}
class Derived1 : Base
{
string DerivedProperty1 { get; set; }
public override bool IsDuplicateOf(Base other)
{
return IsDuplicateOf(other as Derived1);
}
private bool IsDuplicateOf(Derived1 other)
{
return other != null && DerivedProperty1 == other.DerivedProperty1;
}
}
class Derived2 : Base
{
string DerivedProperty2 { get; set; }
public override bool IsDuplicateOf(Base other)
{
return IsDuplicateOf(other as Derived2);
}
private bool IsDuplicateOf(Derived2 other)
{
return other != null && DerivedProperty2 == other.DerivedProperty2;
}
}
您可以在Add
方法中使用该方法:
public void Add(Base baseItem)
{
if(items.Any(x => baseItem.IsDuplicateOf(x)))
throw new DuplicateItemException(...);
items.Add(baseItem);
}
但是请注意,如果列表中有很多项并且IsDuplicateOf
的代码变得更加复杂,则此方法可能会变慢。
如果不先转换为派生类,就无法从基类访问派生类属性。 但是,根据您的情况,您可以做些不同的事情-代替当前的Add
方法(将Base
实例作为参数),创建几个Add
方法重载,每个派生类重载一个:
public void Add(Derived1 item)
{
if(items.OfType<Derived1>().Any(i => i.DerivedProperty1 == item.DerivedProperty1)
throw new InvalidOperationException("An item with the same DerivedProperty1 already exist");
items.Add(baseItem);
}
public void Add(Derived2 item)
{
if(items.OfType<Derived2>().Any(i => i.DerivedProperty2 == item.DerivedProperty2)
throw new InvalidOperationException("An item with the same DerivedProperty2 already exist");
items.Add(baseItem);
}
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