创建<基类>类型的变量存储<派生类>C#中的对象 [英] Creating variable of type <base class> to store <derived class> object in C#

问题描述

我对编程有点陌生，我有一个关于 C# 中的类、继承和多态性的问题.在学习这些主题时，我偶尔会遇到如下代码:

I'm somewhat new to programming and I have a question about classes, inheritance, and polymorphism in C#. While learning about these topics, occasionally I'll come across code that looks something like this:

Animal fluffy = new Cat();  // where Animal is a superclass of Cat*

这让我很困惑，因为我不明白为什么有人会创建一个 Animal 类型的变量来存储 Cat 类型的对象.为什么一个人不简单地写这个:

This confuses me, because I don't understand why someone would create a variable of type Animal to store an object of type Cat. Why wouldn't a person simply write this:

Cat fluffy = new Cat();

我明白为什么将子对象存储在父类型变量中是合法的，但不明白为什么它有用.是否有充分的理由将 Cat 对象存储在 Animal 变量与 Cat 变量中?有人能给我举个例子吗?我确信它与多态性和方法覆盖(和/或方法隐藏)有关，但我似乎无法理解它.提前致谢！

I do understand why it's legal to store a child object in a parent type variable, but not why it's useful. Is there ever a good reason to store a Cat object in an Animal variable vs. a Cat variable? Can a person give me an example? I'm sure it has something to do with polymorphism and method overriding (and/or method hiding) but I can't seem to wrap my head around it. Thanks in advance!

推荐答案

我能给你的最短的例子是如果你想要一个所有动物的列表

The shortest example I can give you is if you want a list of all animals

 List<Animal> Animals = new List<Animal>();
 Animals.Add(new Cat());
 Animals.Add(new Dog());

如果您曾经使用 Winforms 创建过项目，那么您将已经使用过类似的东西，因为所有控件都派生自 Control.然后您会注意到一个窗口有一个控件列表 (this.Controls)，它允许您一次访问窗口上的所有子控件.IE 隐藏所有控件.

If you have ever created a project using Winforms, you will have already used something similar since all controls derive from Control. You will then notice that a Window has a list of controls (this.Controls), that allows you to access all child controls on a window at once. I.E to hide all controls.

 foreach(var control in this.Controls)
      control.Hide();

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