if (listofelements.Contains(valueFieldValue.ToString()))
{
listofelements[listofelements.IndexOf(valueFieldValue.ToString())] = value.ToString();
}
我已经像上面那样替换了。除了这个,还有其他最好的比较方法吗?
if (listofelements.Contains(valueFieldValue.ToString()))
{
listofelements[listofelements.IndexOf(valueFieldValue.ToString())] = value.ToString();
}
我已经像上面那样替换了。除了这个,还有其他最好的比较方法吗?
使用 Lambda 查找 List 中的索引,并使用该索引替换列表项。
List<string> listOfStrings = new List<string> { "abc", "123", "ghi" };
int index = listOfStrings.FindIndex(s => s == "123");
if (index != -1)
listOfStrings[index] = "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;
这仅要求索引一次。您的方法Contains
首先使用需要循环所有项目(在最坏的情况下),然后使用IndexOf
需要再次枚举项目。
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}
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(nameof(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(nameof(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(nameof(source));
return source.Select(x => EqualityComparer<T>.Default.Equals(x, oldValue) ? newValue : x);
}
}
}
添加了前两个方法来更改引用类型的对象。当然,您可以对所有类型只使用第三种方法。
PS 感谢mike 的观察,我添加了 ReplaceAll 方法。
您正在访问您的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;
}
}
按照 rokkuchan 的回答,稍微升级一下:
List<string> listOfStrings = new List<string> {"abc", "123", "ghi"};
int index = listOfStrings.FindIndex(ind => ind.Equals("123"));
if (index > -1)
listOfStrings[index] = "def";
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: - 除了 ThrowIfArgumentIsNull 扩展,您可以使用以下通用方法:
if (argName == null) throw new ArgumentNullException(nameof(argName));
因此,您使用这些扩展的情况可以解决为:
string targetString = valueFieldValue.ToString();
listofelements.Replace(x => x.Equals(targetString), value.ToString());
使用FindIndex
和 lambda 查找和替换您的值:
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
您可以像这样使用 lambda 表达式。
int index = listOfElements.FindIndex(item => item.Id == id);
if (index != -1)
{
listOfElements[index] = newValue;
}
我不知道它是否最好,但你也可以使用它
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,如果您要搜索的项目可以在列表中多次出现::
[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);
}
我发现最好的方法是快速简单
在列表中找到你的项目
var d = Details.Where(x => x.ProductID == selectedProduct.ID).SingleOrDefault();
从当前克隆
OrderDetail dd = d;
更新你的克隆
dd.Quantity++;
在列表中查找索引
int idx = Details.IndexOf(d);
删除 (1) 中的已创建项目
Details.Remove(d);
插入
if (idx > -1)
Details.Insert(idx, dd);
else
Details.Insert(Details.Count, dd);