我在LINQPad中构建了这个:

var listOfNames = new List<string>(){"John","Steve","Anna","Chris"};

var listCount = listOfNames.Count;

var NamesWithCommas = string.Empty;

foreach (var element in listOfNames)
{
    NamesWithCommas += element;
    if(listOfNames.IndexOf(element) != listCount -1)
    {
        NamesWithCommas += ", ";
    }
}

NamesWithCommas.Dump();  //LINQPad method to write to console.

你也可以使用string.join:

var joinResult = string.Join(",", listOfNames);

如果集合是列表，则可以使用list。IndexOf，如:

foreach (Object o in collection)
{
    // ...
    @collection.IndexOf(o)
}

你可以这样写你的循环:

var s = "ABCDEFG";
foreach (var item in s.GetEnumeratorWithIndex())
{
    System.Console.WriteLine("Character: {0}, Position: {1}", item.Value, item.Index);
}

之后添加如下结构和扩展方法。

结构和扩展方法封装了Enumerable。选择功能。

public struct ValueWithIndex<T>
{
    public readonly T Value;
    public readonly int Index;

    public ValueWithIndex(T value, int index)
    {
        this.Value = value;
        this.Index = index;
    }

    public static ValueWithIndex<T> Create(T value, int index)
    {
        return new ValueWithIndex<T>(value, index);
    }
}

public static class ExtensionMethods
{
    public static IEnumerable<ValueWithIndex<T>> GetEnumeratorWithIndex<T>(this IEnumerable<T> enumerable)
    {
        return enumerable.Select(ValueWithIndex<T>.Create);
    }
}

为什么?!

如果你使用List，最简单的方法是使用for而不是foreach:

for (int i = 0 ; i < myList.Count ; i++)
{
    // Do something...
}

或者如果你想使用foreach:

foreach (string m in myList)
{
     // Do something...
}

你可以用它来知道每个循环的索引:

myList.indexOf(m)

我在LINQPad中构建了这个:

var listOfNames = new List<string>(){"John","Steve","Anna","Chris"};

var listCount = listOfNames.Count;

var NamesWithCommas = string.Empty;

foreach (var element in listOfNames)
{
    NamesWithCommas += element;
    if(listOfNames.IndexOf(element) != listCount -1)
    {
        NamesWithCommas += ", ";
    }
}

NamesWithCommas.Dump();  //LINQPad method to write to console.

你也可以使用string.join:

var joinResult = string.Join(",", listOfNames);

这样你就可以使用LINQ来使用索引和值:

ListValues.Select((x, i) => new { Value = x, Index = i }).ToList().ForEach(element =>
{
    // element.Index
    // element.Value
});