c＃，lambda表达式，错误在哪里？

Question

我有这样的方法

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Contacts.xml与它联系的元素。

<Contacts> 
    <Contact> 
     <FirstName>Mike</FirstName> 
     <LastName>Phipps</LastName> 
     <Email>[email protected]</Email> 
    </Contact> 
    <Contact> 
     <FirstName>Holly</FirstName> 
     <LastName>Holt</LastName> 
     <Email>[email protected]</Email> 
    </Contact> 
    <Contact> 
     <FirstName>Liz</FirstName> 
     <LastName>Keyser</LastName> 
    </Contact> 
</Contacts> 

我有这个代码

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; } 
} 

就行了，在那里与“XXXXXX”打上了contact.cs，我应该怎么改线，使其工作？

Answer 1

您Contact类的构造函数需要三个参数 - firstName，lastName和email - 但你试图调用不带参数的构造函数，然后试图设置使用object initializer syntax属性。

要解决它，你需要将三个参数传递到构造函数本身：

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

Answer 2

我认为你缺少联系的公共构造。

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; } 
} 

或者只是使用现有的构造函数。