如何以最佳方式替换列表项

if (listofelements.Contains(valueFieldValue.ToString()))
{
    listofelements[listofelements.IndexOf(valueFieldValue.ToString())] = value.ToString();
}

我已经像上面一样替换了。除此以外，还有其他最佳方法吗？

使用Lambda在列表中找到索引，然后使用该索引替换列表项。

List<string> listOfStrings = new List<string> {"abc", "123", "ghi"};
listOfStrings[listOfStrings.FindIndex(ind=>ind.Equals("123"))] =  "def";

您可以使其更具可读性和效率：

string oldValue = valueFieldValue.ToString();
string newValue = value.ToString();
int index = listofelements.IndexOf(oldValue);
if(index != -1)
    listofelements[index] = newValue;

这只要求一次索引。您的方法使用Contains首先需要循环所有项目的方法（在最坏的情况下），然后使用IndexOf需要再次枚举项目的方法。

您要访问列表两次以替换一个元素。我认为简单的for循环就足够了：

var key = valueFieldValue.ToString();
for (int i = 0; i < listofelements.Count; i++)
{
    if (listofelements[i] == key)
    {
        listofelements[i] = value.ToString();
        break;
    }
}

为什么不使用扩展方法？

考虑以下代码：

        var intArray = new int[] { 0, 1, 1, 2, 3, 4 };
        // Replaces the first occurance and returns the index
        var index = intArray.Replace(1, 0);
        // {0, 0, 1, 2, 3, 4}; index=1

        var stringList = new List<string> { "a", "a", "c", "d"};
        stringList.ReplaceAll("a", "b");
        // {"b", "b", "c", "d"};

        var intEnum = intArray.Select(x => x);
        intEnum = intEnum.Replace(0, 1);
        // {0, 0, 1, 2, 3, 4} => {1, 1, 1, 2, 3, 4}

• 没有代码重复
• 无需键入长linq表达式
• 无需额外使用

源代码：

namespace System.Collections.Generic
{
    public static class Extensions
    {
        public static int Replace<T>(this IList<T> source, T oldValue, T newValue)
        {
            if (source == null)
                throw new ArgumentNullException("source");

            var index = source.IndexOf(oldValue);
            if (index != -1)
                source[index] = newValue;
            return index;
        }

        public static void ReplaceAll<T>(this IList<T> source, T oldValue, T newValue)
        {
            if (source == null)
                throw new ArgumentNullException("source");

            int index = -1;
            do
            {
                index = source.IndexOf(oldValue);
                if (index != -1)
                    source[index] = newValue;
            } while (index != -1);
        }


        public static IEnumerable<T> Replace<T>(this IEnumerable<T> source, T oldValue, T newValue)
        {
            if (source == null)
                throw new ArgumentNullException("source");

            return source.Select(x => EqualityComparer<T>.Default.Equals(x, oldValue) ? newValue : x);
        }
    }
}

添加了前两种方法以更改引用类型的对象。当然，您可以对所有类型仅使用第三种方法。

PS由于mike的观察，我添加了ReplaceAll方法。

按照rokkuchan的回答，只需稍作升级：

List<string> listOfStrings = new List<string> {"abc", "123", "ghi"};

int index = listOfStrings.FindIndex(ind => ind.Equals("123"));
if (index > -1)
    listOfStrings[index] =  "def";

使用FindIndex和lambda查找并替换您的值：

int j = listofelements.FindIndex(i => i.Contains(valueFieldValue.ToString())); //Finds the item index

lstString[j] = lstString[j].Replace(valueFieldValue.ToString(), value.ToString()); //Replaces the item by new value

您可以使用基于谓词条件的下一个扩展：

    /// <summary>
    /// Find an index of a first element that satisfies <paramref name="match"/>
    /// </summary>
    /// <typeparam name="T">Type of elements in the source collection</typeparam>
    /// <param name="this">This</param>
    /// <param name="match">Match predicate</param>
    /// <returns>Zero based index of an element. -1 if there is not such matches</returns>
    public static int IndexOf<T>(this IList<T> @this, Predicate<T> match)
    {
        @this.ThrowIfArgumentIsNull();
        match.ThrowIfArgumentIsNull();

        for (int i = 0; i < @this.Count; ++i)
            if (match(@this[i]))
                return i;

        return -1;
    }

    /// <summary>
    /// Replace the first occurance of an oldValue which satisfies the <paramref name="removeByCondition"/> by a newValue
    /// </summary>
    /// <typeparam name="T">Type of elements of a target list</typeparam>
    /// <param name="this">Source collection</param>
    /// <param name="removeByCondition">A condition which decides is a value should be replaced or not</param>
    /// <param name="newValue">A new value instead of replaced</param>
    /// <returns>This</returns>
    public static IList<T> Replace<T>(this IList<T> @this, Predicate<T> replaceByCondition, T newValue)
    {
        @this.ThrowIfArgumentIsNull();
        removeByCondition.ThrowIfArgumentIsNull();

        int index = @this.IndexOf(replaceByCondition);
        if (index != -1)
            @this[index] = newValue;

        return @this;
    }

    /// <summary>
    /// Replace all occurance of values which satisfy the <paramref name="removeByCondition"/> by a newValue
    /// </summary>
    /// <typeparam name="T">Type of elements of a target list</typeparam>
    /// <param name="this">Source collection</param>
    /// <param name="removeByCondition">A condition which decides is a value should be replaced or not</param>
    /// <param name="newValue">A new value instead of replaced</param>
    /// <returns>This</returns>
    public static IList<T> ReplaceAll<T>(this IList<T> @this, Predicate<T> replaceByCondition, T newValue)
    {
        @this.ThrowIfArgumentIsNull();
        removeByCondition.ThrowIfArgumentIsNull();

        for (int i = 0; i < @this.Count; ++i)
            if (replaceByCondition(@this[i]))
                @this[i] = newValue;

        return @this;
    }

注意：-代替ThrowIfArgumentIsNull扩展，可以使用如下通用方法：

if (argName == null) throw new ArgumentNullException(nameof(argName));

因此，使用这些扩展名的情况可以解决为：

string targetString = valueFieldValue.ToString();
listofelements.Replace(x => x.Equals(targetString), value.ToString());

我不是最好还是不是，但您也可以使用它

List<string> data = new List<string>
(new string[]   { "Computer", "A", "B", "Computer", "B", "A" });
int[] indexes = Enumerable.Range(0, data.Count).Where
                 (i => data[i] == "Computer").ToArray();
Array.ForEach(indexes, i => data[i] = "Calculator");

或者，根据Rusian L.的建议，如果要搜索的项目可以多次出现在列表中：

[Extension()]
public void ReplaceAll<T>(List<T> input, T search, T replace)
{
    int i = 0;
    do {
        i = input.FindIndex(i, s => EqualityComparer<T>.Default.Equals(s, search));

        if (i > -1) {
            FileSystem.input(i) = replace;
            continue;
        }

        break;  
    } while (true);
}

您可以像这样使用lambda表达式。

int index = listOfElements.FindIndex(item => item.Id == id);  
if (index != -1) 
{
    listOfElements[index] = newValue;
}

我发现最适合快速简便地做到这一点

1. 在列表中找到您的项目

   var d = Details.Where(x => x.ProductID == selectedProduct.ID).SingleOrDefault();

2. 从当前克隆

   OrderDetail dd = d;

3. 更新您的克隆

   dd.Quantity++;

4. 在列表中查找索引

   int idx = Details.IndexOf(d);

5. 删除（1）中的已建立项目

     Details.Remove(d);

6. 插

    if (idx > -1)
         Details.Insert(idx, dd);
     else
         Details.Insert(Details.Count, dd);