How to replace list item in best way

Question

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

Answer 1

I don't if it is best or not but you can use it also

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");

Answer 2

Or, building on Rusian L.'s suggestion, if the item you're searching for can be in the list more than once::

[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);
}

Answer 3

i find best for do it fast and simple

1. find ur item in list

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

2. make clone from current

   OrderDetail dd = d;
   

3. Update ur clone

   dd.Quantity++;
   

4. find index in list

   int idx = Details.IndexOf(d);
   

5. remove founded item in (1)

     Details.Remove(d);
   

6. insert

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

Answer 4

Use Lambda to find the index in the List and use this index to replace the list item.

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

Answer 5

You can use the next extensions which are based on a predicate condition:

    /// <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;
    }

Notes: - Instead of ThrowIfArgumentIsNull extension, you can use a general approach like:

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

So your case with these extensions can be solved as:

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