如何在 C# 中进行构造函数链接 [英] How to do constructor chaining in C#

问题描述

我知道这应该是一个非常简单的问题，但我已经在这个概念上挣扎了一段时间.

I know that this is supposedly a super simple question, but I've been struggling with the concept for some time now.

我的问题是，你如何在 C# 中链接构造函数?

My question is, how do you chain constructors in C#?

我在上我的第一个 OOP 课程，所以我只是在学习.我不明白构造函数链接是如何工作的，或者如何实现它，甚至不明白为什么它比只做没有链接的构造函数更好.

I'm in my first OOP class, so I'm just learning. I don't understand how constructor chaining works or how to implement it or even why it's better than just doing constructors without chaining.

我会很感激一些带有解释的例子.

I would appreciate some examples with an explanation.

那么如何链接它们呢?
我知道有两个:

So how do how chain them?
I know with two it goes:

public SomeClass this: {0}

public SomeClass
{
    someVariable = 0
} 

但是你如何用三个、四个等等来做到这一点?

But how do you do it with three, four and so on?

同样，我知道这是一个初学者问题，但我很难理解这一点，我不知道为什么.

Again, I know this is a beginner question, but I'm struggling to understand this and I don't know why.

推荐答案

您使用标准语法(使用 this 就像一个方法)来选择重载，内部类:

You use standard syntax (using this like a method) to pick the overload, inside the class:

class Foo 
{
    private int id;
    private string name;

    public Foo() : this(0, "") 
    {
    }

    public Foo(int id, string name) 
    {
        this.id = id;
        this.name = name;
    }

    public Foo(int id) : this(id, "") 
    {
    }

    public Foo(string name) : this(0, name) 
    {
    }
}

然后:

Foo a = new Foo(), b = new Foo(456,"def"), c = new Foo(123), d = new Foo("abc");

还要注意:

• 您可以使用 base(...)
链接到基类型上的构造函数
• 你可以在每个构造函数中加入额外的代码
• 默认值(如果您没有指定任何内容)是 base()

对于为什么?":

• 代码减少(总是一件好事)

• 需要来调用一个非默认的基础构造函数，例如:

• code reduction (always a good thing)

• necessary to call a non-default base-constructor, for example:

SomeBaseType(int id) : base(id) {...}

请注意，您也可以以类似的方式使用对象初始值设定项(无需编写任何内容):

Note that you can also use object initializers in a similar way, though (without needing to write anything):

SomeType x = new SomeType(), y = new SomeType { Key = "abc" },
         z = new SomeType { DoB = DateTime.Today };

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