我就是这么做的，这很简单，但如果你在循环body obj中做了很多。价值，它很快就会过时。

foreach(var obj in collection.Select((item, index) => new { Index = index, Value = item }) {
    string foo = string.Format("Something[{0}] = {1}", obj.Index, obj.Value);
    ...
}

我不认为这应该很有效，但它确实有效:

@foreach (var banner in Model.MainBanners) {
    @Model.MainBanners.IndexOf(banner)
}

这是我刚想到的解决这个问题的办法

原始代码:

int index=0;
foreach (var item in enumerable)
{
    blah(item, index); // some code that depends on the index
    index++;
}

更新代码

enumerable.ForEach((item, index) => blah(item, index));

扩展方法:

    public static IEnumerable<T> ForEach<T>(this IEnumerable<T> enumerable, Action<T, int> action)
    {
        var unit = new Unit(); // unit is a new type from the reactive framework (http://msdn.microsoft.com/en-us/devlabs/ee794896.aspx) to represent a void, since in C# you can't return a void
        enumerable.Select((item, i) => 
            {
                action(item, i);
                return unit;
            }).ToList();

        return pSource;
    }

我对这个问题的解决方案是一个扩展方法WithIndex()，

http://code.google.com/p/ub-dotnet-utilities/source/browse/trunk/Src/Utilities/Extensions/EnumerableExtensions.cs

像这样使用它

var list = new List<int> { 1, 2, 3, 4, 5, 6 };    

var odd = list.WithIndex().Where(i => (i.Item & 1) == 1);
CollectionAssert.AreEqual(new[] { 0, 2, 4 }, odd.Select(i => i.Index));
CollectionAssert.AreEqual(new[] { 1, 3, 5 }, odd.Select(i => i.Item));

我想更理论化地讨论这个问题(因为它已经有了足够多的实际答案)

.net为数据组(又称集合)提供了一个非常好的抽象模型。

在最顶端，也是最抽象的，你有一个IEnumerable它只是一组你可以枚举的数据。你如何枚举并不重要，重要的是你可以枚举一些数据。这个枚举是由一个完全不同的对象完成的，IEnumerator

这些接口定义如下:

//
// Summary:
//     Exposes an enumerator, which supports a simple iteration over a non-generic collection.
public interface IEnumerable
{
    //
    // Summary:
    //     Returns an enumerator that iterates through a collection.
    //
    // Returns:
    //     An System.Collections.IEnumerator object that can be used to iterate through
    //     the collection.
    IEnumerator GetEnumerator();
}

//
// Summary:
//     Supports a simple iteration over a non-generic collection.
public interface IEnumerator
{
    //
    // Summary:
    //     Gets the element in the collection at the current position of the enumerator.
    //
    // Returns:
    //     The element in the collection at the current position of the enumerator.
    object Current { get; }

    //
    // Summary:
    //     Advances the enumerator to the next element of the collection.
    //
    // Returns:
    //     true if the enumerator was successfully advanced to the next element; false if
    //     the enumerator has passed the end of the collection.
    //
    // Exceptions:
    //   T:System.InvalidOperationException:
    //     The collection was modified after the enumerator was created.
    bool MoveNext();
    //
    // Summary:
    //     Sets the enumerator to its initial position, which is before the first element
    //     in the collection.
    //
    // Exceptions:
    //   T:System.InvalidOperationException:
    //     The collection was modified after the enumerator was created.
    void Reset();
}

as you might have noticed, the IEnumerator interface doesn't "know" what an index is, it just knows what element it's currently pointing to, and how to move to the next one. now here is the trick: foreach considers every input collection an IEnumerable, even if it is a more concrete implementation like an IList<T> (which inherits from IEnumerable), it will only see the abstract interface IEnumerable. what foreach is actually doing, is calling GetEnumerator on the collection, and calling MoveNext until it returns false. so here is the problem, you want to define a concrete concept "Indices" on an abstract concept "Enumerables", the built in foreach construct doesn't give you that option, so your only way is to define it yourself, either by what you are doing originally (creating a counter manually) or just use an implementation of IEnumerator that recognizes indices AND implement a foreach construct that recognizes that custom implementation.

就我个人而言，我会创建一个这样的扩展方法

public static class Ext
{
    public static void FE<T>(this IEnumerable<T> l, Action<int, T> act)
    {
        int counter = 0;
        foreach (var item in l)
        {
            act(counter, item);
            counter++;
        }
    }
}

像这样使用它

var x = new List<string>() { "hello", "world" };
x.FE((ind, ele) =>
{
    Console.WriteLine($"{ind}: {ele}");
});

这也避免了在其他答案中看到的任何不必要的分配。

最后，c# 7有一个不错的语法，用于在foreach循环(即元组)中获取索引:

foreach (var (item, index) in collection.WithIndex())
{
    Debug.WriteLine($"{index}: {item}");
}

需要一个小扩展方法:

using System.Collections.Generic;

public static class EnumExtension {
    public static IEnumerable<(T item, int index)> WithIndex<T>(this IEnumerable<T> self)       
       => self.Select((item, index) => (item, index));
}