处理只读 List<T> 时应该如何使用属性?成员 [英] How should I use properties when dealing with read-only List<T> members

问题描述

当我想在我的课外将值类型设为只读时，我会这样做:

When I want to make a value type read-only outside of my class I do this:

public class myClassInt
{
    private int m_i;
    public int i {
        get { return m_i; }
    }

    public myClassInt(int i)
    {
        m_i = i;
    }
}

我该怎么做才能在我的班级之外使 List 类型成为只读(这样他们就不能在其中添加/删除元素)?现在我只是宣布它是公开的:

What can I do to make a List<T> type readonly (so they can't add/remove elements to/from it) outside of my class? Now I just declare it public:

public class myClassList
{
    public List<int> li;
    public  myClassList()
    {
        li = new List<int>();
        li.Add(1);
        li.Add(2);
        li.Add(3);
    }
}

推荐答案

你可以公开它 作为只读.也就是说，返回一个只读的 IList 包装器.例如...

You can expose it AsReadOnly. That is, return a read-only IList<T> wrapper. For example ...

public ReadOnlyCollection<int> List
{
    get { return _lst.AsReadOnly(); }
}

仅仅返回一个 IEnumerable 是不够的.例如...

Just returning an IEnumerable<T> is not sufficient. For example ...

void Main()
{
    var el = new ExposeList();
    var lst = el.ListEnumerator;
    var oops = (IList<int>)lst;
    oops.Add( 4 );  // mutates list

    var rol = el.ReadOnly;
    var oops2 = (IList<int>)rol;

    oops2.Add( 5 );  // raises exception
}

class ExposeList
{
  private List<int> _lst = new List<int>() { 1, 2, 3 };

  public IEnumerable<int> ListEnumerator
  {
     get { return _lst; }
  }

  public ReadOnlyCollection<int> ReadOnly
  {
     get { return _lst.AsReadOnly(); }
  }
}

史蒂夫的回答 还有一个巧妙的方法来避免强制转换.

Steve's answer also has a clever way to avoid the cast.

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