c# - 将基类转换为派生类

Question

我想知道为什么这会适本地填充派生类:

BaseClass bc = MethodThatReturnsBaseClassObject();
DerivedClass dc = bc as DerivedClass;

但这会创建一个空派生类对象:

DerivedClass dc = MethodThatReturnsBaseClassObject() as DerivedClass;

Answer 1

这是因为 BaseClass 不是 DerivedClass 的实例(但是 DerivedClass 是 BaseClass 的实例) ，因此您不能将基类的实例转换为派生类的实例(好吧，您可以，但如您所见，它将为 null)。

您可以通过向将基类作为参数的派生类添加构造函数来实现(我认为)您想要实现的目标:

public DerivedClass(BaseClass baseClass) {
    // Populate common properties, call other derived class constructor, or call base constructor
}

然后:

 DerivedClass dc = new DerivedClass(MethodThatReturnsBaseClassObject());