如何在 C# 中的自定义对象上使用 foreach 关键字 [英] How to use foreach keyword on custom Objects in C#

问题描述

有人可以分享一个将 foreach 关键字用于自定义对象的简单示例吗?

Can someone share a simple example of using the foreach keyword with custom objects?

推荐答案

鉴于标签，我假设您的意思是在 .NET 中 - 我将选择谈论 C#，因为这就是我所知道的.

Given the tags, I assume you mean in .NET - and I'll choose to talk about C#, as that's what I know about.

foreach 语句(通常)使用 IEnumerable 和 IEnumerator 或它们的通用表兄弟.声明形式:

The foreach statement (usually) uses IEnumerable and IEnumerator or their generic cousins. A statement of the form:

foreach (Foo element in source)
{
    // Body
}

其中source实现IEnumerable大致等价于:

using (IEnumerator<Foo> iterator = source.GetEnumerator())
{
    Foo element;
    while (iterator.MoveNext())
    {
        element = iterator.Current;
        // Body
    }
}

请注意，IEnumerator 放在最后，但是语句会退出.这对于迭代器块很重要.

Note that the IEnumerator<Foo> is disposed at the end, however the statement exits. This is important for iterator blocks.

要自己实现 IEnumerable 或 IEnumerator，最简单的方法是使用迭代器块.与其在这里写下所有的细节，不如让你参考深入了解 C# 的第 6 章，这是一个免费下载.整个第 6 章都是关于迭代器的.我的 C# in Depth 网站上还有另外几篇文章:

To implement IEnumerable<T> or IEnumerator<T> yourself, the easiest way is to use an iterator block. Rather than write all the details here, it's probably best to just refer you to chapter 6 of C# in Depth, which is a free download. The whole of chapter 6 is on iterators. I have another couple of articles on my C# in Depth site, too:

• 迭代器、迭代器块和数据管道
• 迭代器块实现细节

举个简单的例子:

public IEnumerable<int> EvenNumbers0To10()
{
    for (int i=0; i <= 10; i += 2)
    {
        yield return i;
    }
}

// Later
foreach (int x in EvenNumbers0To10())
{
    Console.WriteLine(x); // 0, 2, 4, 6, 8, 10
}

要为类型实现 IEnumerable，您可以执行以下操作:

To implement IEnumerable<T> for a type, you can do something like:

public class Foo : IEnumerable<string>
{
    public IEnumerator<string> GetEnumerator()
    {
        yield return "x";
        yield return "y";
    }

    // Explicit interface implementation for nongeneric interface
    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator(); // Just return the generic version
    }
}

这篇关于如何在 C# 中的自定义对象上使用 foreach 关键字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！