自动属性和构造函数的意外 C# 行为
我花了一些调试才弄清楚这一点（或者我是这么认为的）。我会将代码交给您，看看您能想到什么。有一个简单的 Contact 类，其中包含：
- 一些自动属性，
- 一个参数化构造函数，它始终递增
Contact.ID属性，并根据它获得的参数设置其他属性 - 无参数构造函数总是使用默认值调用参数化构造函数。
首先看代码；其输出和问题遵循以下代码：
using System;
class Program
{
private static void Main(string[] args)
{
Contact[] contacts_array = {
//Contact 0
new Contact(),
//Contact 1
new Contact {
Name = "contactName1",
Age = 40,
Email = "[email protected]"
},
//Contact 2
new Contact {
Name = "contactName2",
Age = 41,
Email = "[email protected]"
},
//Contact 3
new Contact("contactName3",
42,
"[email protected]"),
};
foreach (var contact in contacts_array)
Console.WriteLine(contact);
Console.ReadLine();
}
}
public class Contact
{
public static int totalContacts = 0;
public int Id { get; private set; }
public string Name { get; set; }
public int? Age { get; set; }
public string Email { get; set; }
public Contact()
{
new Contact("ANONYMOUS", null, "[email protected]");
}
public Contact(string name, int? age, string email)
{
Id = Contact.totalContacts++;
Name = name;
Age = age;
Email = email;
}
public override string ToString()
{
return string.Format("[Contact: Id={0}, Name={1}, Age={2}, Email={3}]",
Id, Name, Age, Email);
}
}
输出：
[Contact: Id=0, Name=, Age=, Email=]
[Contact: Id=0, Name=contactName1, Age=40, [email protected]]
[Contact: Id=0, Name=contactName2, Age=41, [email protected]]
[Contact: Id=3, Name=contactName3, Age=42, [email protected]]
问题：
为什么第二个和第三个联系人中的 Contact.ID == 0 而分别是 1 和 2，尽管参数化构造函数总是被调用并且总是增加 ID 属性？
It took me some debugging to figure this out (or so do I think). I will let the code loose on you and see what you come up with. There is a simple Contact class with:
- Some auto-properties,
- A parameterized constructor which always increments the
Contact.IDproperty and sets other properties according to the arguments it gets - A parameterless constructor which always calls the parameterized constructor with default values.
First see the code; its output and the question follows the code:
using System;
class Program
{
private static void Main(string[] args)
{
Contact[] contacts_array = {
//Contact 0
new Contact(),
//Contact 1
new Contact {
Name = "contactName1",
Age = 40,
Email = "[email protected]"
},
//Contact 2
new Contact {
Name = "contactName2",
Age = 41,
Email = "[email protected]"
},
//Contact 3
new Contact("contactName3",
42,
"[email protected]"),
};
foreach (var contact in contacts_array)
Console.WriteLine(contact);
Console.ReadLine();
}
}
public class Contact
{
public static int totalContacts = 0;
public int Id { get; private set; }
public string Name { get; set; }
public int? Age { get; set; }
public string Email { get; set; }
public Contact()
{
new Contact("ANONYMOUS", null, "[email protected]");
}
public Contact(string name, int? age, string email)
{
Id = Contact.totalContacts++;
Name = name;
Age = age;
Email = email;
}
public override string ToString()
{
return string.Format("[Contact: Id={0}, Name={1}, Age={2}, Email={3}]",
Id, Name, Age, Email);
}
}
Output:
[Contact: Id=0, Name=, Age=, Email=]
[Contact: Id=0, Name=contactName1, Age=40, [email protected]]
[Contact: Id=0, Name=contactName2, Age=41, [email protected]]
[Contact: Id=3, Name=contactName3, Age=42, [email protected]]
Question:
Why is the Contact.ID == 0 in the second and third contacts rather being 1 and 2 respectively, despite the parameterized constructor being always called and always increment the ID property?
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评论（1）
您的默认构造函数不会执行您认为的操作：
这将构造一个新的
Contact，然后丢弃它，当前实例将获得所有默认值。这是您需要的语法：Your default constructor doesn't do what you think it does:
This will construct a new
Contactand then discard it, the current instance will get all default values. Here is the syntax you're after: