铸造列表< MyObject>到IEnumerable< MyInterface> [英] Casting List<MyObject> to IEnumerable<MyInterface>

问题描述

我仍然在学习一些这个c＃的东西，我找不到这个问题的答案。假设我有一个MyObject实现MyInterface的列表

I'm still learning some of this c# stuff, and I couldn't find an answer to this question. Assuming that I have a list of MyObject implementing MyInterface

public class MyObject : IMyInterface { ...}

public List<MyObject> MyObjectList;

如何返回 IEnumerable< IMyInterface> 与MyObjectList的内容？

How can I return an IEnumerable<IMyInterface> with the contents of MyObjectList?

我的意思是，现在我有这个：

I mean, right now I have this:

List<IMyInterface> temp = new List<IMyInterface>();
foreach (MyObject obj in MyObjects) temp.Add(obj);
return (IEnumerable<IMyInterface>)temp;

但是是否需要创建一个这样的新列表？

But is it necessary to create a new list like this?

谢谢。

推荐答案

如果使用.NET 3.5，最简单的方法是：

If you're using .NET 3.5, the easiest way to do this is:

return MyObjects.Cast<IMyInterface>();

你不需要创建一切的副本 - 但直到C＃4出来的通用

You don't need to create a copy of everything - but until C# 4 comes out with its generic interface variance, you're stuck doing something like this.

如果你还在使用.NET 2.0，你可以很容易做类似的事情：

If you're still using .NET 2.0, you can easily do something similar:

public static IEnumerable<TResult> SafeCast<TSource, TResult>
    (IEnumerable<TSource> source) where TResult : TSource
{
    foreach (TSource item in source)
    {
        yield return item;
    }
}

（请注意，这不会检查 source 为null;要正确地做，你会想要两个方法，由于延迟执行迭代器块。）

(Note that this doesn't check for source being null; to do that properly you'd want two methods due to the deferred execution of iterator blocks.)

然后使用：

return SafeCast<MyObject, IMyInterface>(MyObjects);

您可以使其更像LINQ版本， / p>

You could make it more like the LINQ version, like this:

public static IEnumerable<T> SafeCast<T>(IEnumerable source)
{
    foreach (T item in source)
    {
        yield return item;
    }
}

return SafeCast<IMyInterface>(MyObjects);

这有编译时的安全性 - 它不会阻止你尝试转换例如

This has compile-time safety though - it wouldn't stop you from trying to convert a List<string> into an IEnumerable<Guid> for example.

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