Question

我有一个object，它有一些属性，其中一些属性是Lists。每个列表都包含其他类的实例。我想要做的是从列表中取出第一项并覆盖这些属性值。

这是我所拥有的一个伪示例：

public class User
{
    public List<Address> Addresses = new List<Address>();

    public User ( )
    {
        Addresses = fill with data;
    }
}


public class TestUser
{
    public User user; // Is filled somewhere in this class

    public void TestUpdateList ( Address addr )
    {
        // The param "addr" contains new values
        // These values must ALWAYS be placed in the first item
        // of the "Addresses" list.

        // Get the first Address object and overwrite that with
        // the new "addr" object
        user.Addresses[0] = addr; // <-- doesn't work, but should give you an idea
    }
}

我希望这个例子能说明我想做什么。

所以我基本上在寻找一种方法来“更新”列表中的现有项目，在这种情况下是object。

Answer 1

您的示例无法编译，因为您通过类名访问Addresses属性。只有在它是静态的情况下才有可能。所以你首先需要一个用户的实例来更新他的地址：

User u = new User(userID); // assuming that theres a constructor that takes an identifier
u.Addresses[0] = addr;

C# Language Specification: 10.2.5 Static and instance members

Answer 2

目前还不完全清楚您要完成的任务，但是，请参阅以下代码 - 有一个地址，一个用户和一个名为FeatureX的实用程序，它替换了具有给定值的用户的第一个地址。 / p>

class Address {
    public string Street { get; set; }
}

class User {
    public List<Address> Addresses = new List<Address>();
}

class FeatureX {
    public void UpdateUserWithAddress(User user, Address address) {
        if (user.Addresses.Count > 0) {
            user.Addresses[0] = address;
        } else {
            user.Addresses.Add(address);
        }
    }
}

以下用法输出'Xyz'两次：

User o = new User();
Address a = new Address() { Street = "Xyz" };

new FeatureX().UpdateUserWithAddress(o, a);
Console.WriteLine(o.Addresses[0].Street);

o = new User();
o.Addresses.Add(new Address { Street = "jjj" });
new FeatureX().UpdateUserWithAddress(o, a);
Console.WriteLine(o.Addresses[0].Street);

请注意，如果您与第三方共享DLL，公共字段可能会造成很多麻烦。

Answer 3

我认为问题在于地址是一个私人领域。

这有效：

[TestFixture]
public class ListTest
{
    [Test]
    public void UpdateTest()
    {
        var user = new User();
        user.Addresses.Add(new Address{Name = "Johan"});
        user.Addresses[0] = new Address { Name = "w00" };
    }
}
public class User
{
    public List<Address> Addresses { get;private  set; }

    public User()
    {
        Addresses= new List<Address>();
    }
}
public class Address
{
    public string Name { get; set; }
}

Answer 4

public void TestUpdateList ( User user, Address addr )
    {
        // The param "addr" contains new values
        // These values must ALWAYS be placed in the first item
        // of the "Addresses" list.

        // Get the first Address object and overwrite that with
        // the new "addr" object
        user.Addresses[0] = addr; // <-- doesn't work, but should give you an idea
    }

C＃ - 使用新对象值更新列表项

4 个答案: