C# - 何时使用 public int virtual，何时仅使用 public int

Question

我正在学习 J Galloway 的教程“Professional ASP.NET MVC 3”。在本教程中，Jon 向我们展示了如何构建 MVC 音乐商店。

我正在创建 CS 类以首先使用 EF 代码对数据建模。

我所有书中的例子，public virtual int property {get;放; 的使用没有任何解释。虚拟一词随处可见。

在网络的其他地方，我没有看到以任何形式的一致性使用“虚拟”一词。

谁能给我解释一下:

1. “虚拟”一词在此特定上下文中的用途
2. 是否有必要使用“虚拟”？
3. 为什么有些人使用“虚拟”而有些人不使用？
4. 为什么有些人在定义外键时只使用“虚拟”？
5. 使用“虚拟”一词的最佳做法是什么？

提前致谢

Answer 1

为了真正理解 virtual 关键字，您需要阅读 Polymorphism in general :

Polymorphism is often referred to as the third pillar of object-oriented programming, after encapsulation and inheritance. Polymorphism is a Greek word that means "many-shaped" and it has two distinct aspects:

1. At run time, objects of a derived class may be treated as objects of a base class in places such as method parameters and collections or arrays. When this occurs, the object's declared type is no longer identical to its run-time type.

2. Base classes may define and implement virtual methods, and derived classes can override them, which means they provide their own definition and implementation. At run-time, when client code calls the method, the CLR looks up the run-time type of the object, and invokes that override of the virtual method. Thus in your source code you can call a method on a base class, and cause a derived class's version of the method to be executed.

一旦您更好地理解了这些概念，您就可以确定您根据本书创建的方法是否需要虚拟。