Question

我有这个方法

    public static List<Contact> Load(string filename)
    {
        if (!File.Exists(filename))
        {
            throw new FileNotFoundException("Data file could not be found", filename);

        }
        var contacts = 
            System.Xml.Linq.XDocument.Load(filename).Root.Elements("Contact").Select
            (
                x => new Contact() { //errors out here, XXXXXX
                            FirstName = (string)x.Element("FirstName"),
                            LastName = (string)x.Element("LastName"),
                            Email = (string)x.Element("Email")
                         }
            );
        return contacts.ToList();// is this line correct?, it should return List...
    }

我的Contacts.xml中包含Contact元素。

<Contacts>
    <Contact>
        <FirstName>Mike</FirstName>
        <LastName>Phipps</LastName>
        <Email>mike@contoso.com</Email>
    </Contact>
    <Contact>
        <FirstName>Holly</FirstName>
        <LastName>Holt</LastName>
        <Email>holly@contoso.com</Email>
    </Contact>
    <Contact>
        <FirstName>Liz</FirstName>
        <LastName>Keyser</LastName>
    </Contact>
</Contacts>

我有一个使用此代码的contact.cs

public class Contact
{
    public Contact(string firstName, string lastName, string email)
    {
        FirstName = firstName;
        LastName = lastName;
        Email = email;
    }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Email { get; set; }
    public string PhoneNumber { get; set; }
    public string Address { get; set; }
}

在线上，标有'XXXXXX'，我应该如何更改线路才能使其正常工作？

Answer 1

Contact类的构造函数需要三个参数 - firstName，lastName和email - 但是您试图在没有参数的情况下调用构造函数然后尝试使用object initializer syntax设置属性。

要修复它，您需要将三个参数传递给构造函数本身：

x => new Contact(
    (string)x.Element("FirstName"),
    (string)x.Element("LastName"),
    (string)x.Element("Email"));

Answer 2

我认为你错过了Contact中的公共构造函数。

public class Contact
{
    public Contact() {}

    public Contact(string firstName, string lastName, string email) {
        FirstName = firstName;
        LastName = lastName;
        Email = email;
    }

    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Email { get; set; }
    public string PhoneNumber { get; set; }
    public string Address { get; set; }
}

或者只使用现有的构造函数。

c＃，lambda表达式，错误在哪里？

2 个答案: