只读集合属性的 C# 对象初始化 [英] C# object initialization of read only collection properties

问题描述

在我的一生中，我无法弄清楚下面的 C# 代码示例中发生了什么.测试类的集合 (List) 属性设置为只读，但我似乎可以在对象初始值设定项中分配给它.

For the life of me, I cannot figure out what is going on in the example piece of C# code below. The collection (List) property of the test class is set as read only, but yet I can seemingly assign to it in the object initializer.

** 修复了 List 'getter' 的问题

** Fixed the problem with the List 'getter'

using System;
using System.Collections.Generic;
using NUnit.Framework;

namespace WF4.UnitTest
{
    public class MyClass
    {
        private List<string> _strCol = new List<string> {"test1"};

        public List<string> StringCollection 
        {
            get
            {
                return _strCol;
            }
        }
    }

    [TestFixture]
    public class UnitTests
    {
        [Test]
        public void MyTest()
        {
            MyClass c = new MyClass
            {
                // huh?  this property is read only!
                StringCollection = { "test2", "test3" }
            };

            // none of these things compile (as I wouldn't expect them to)
            //c.StringCollection = { "test1", "test2" };
            //c.StringCollection = new Collection<string>();

            // 'test1', 'test2', 'test3' is output
            foreach (string s in c.StringCollection) Console.WriteLine(s);
        }
    }
}

推荐答案

这个:

MyClass c = new MyClass
{
    StringCollection = { "test2", "test3" }
};

翻译成这样:

MyClass tmp = new MyClass();
tmp.StringCollection.Add("test2");
tmp.StringCollection.Add("test3");
MyClass c = tmp;

它从不尝试调用 setter - 它只是根据调用 getter 的结果调用 Add.请注意，它也不会清除原始集合.

It's never trying to call a setter - it's just calling Add on the results of calling the getter. Note that it's also not clearing the original collection either.

这在 C# 4 规范的第 7.6.10.3 节中有更详细的描述.

This is described in more detail in section 7.6.10.3 of the C# 4 spec.

作为一个兴趣点，我对它两次调用 getter 感到有些惊讶.我希望它调用 getter 一次，然后调用 Add 两次......规范包含一个演示这一点的示例.

Just as a point of interest, I was slightly surprised that it calls the getter twice. I expected it to call the getter once, and then call Add twice... the spec includes an example which demonstrates that.

这篇关于只读集合属性的 C# 对象初始化的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！