How Can I Use a Custom IComparer to Correctly Sort Objects in LINQ OrderBy?

Using Custom IComparer for Linq OrderBy

Problem:

You have a list of objects with a property containing invoice numbers in a specific string format, e.g., 200906/1. The default sorting of Linq OrderBy in C# results in an undesirable sorting order, such as 200906/1, 200906/10, 200906/11.

Solution:

To implement your own custom sorting order, you can define an IComparer interface implementation. Here's a sample implementation:

public class MyComparer : IComparer<Object>
{
    public int Compare(Object stringA, Object stringB)
    {
        string[] valueA = stringA.ToString().Split('/');
        string[] valueB = stringB.ToString().Split('/');

        if (valueA.Length != 2 || valueB.Length != 2)
        {
            return stringA.ToString().CompareTo(stringB.ToString());
        }

        // Parse numbers for comparison
        int numA = int.Parse(valueA[0]);
        int numB = int.Parse(valueB[0]);
        if (numA == numB) 
        {
            return int.Parse(valueA[1]).CompareTo(int.Parse(valueB[1]));
        }
        else
        {
            return numA.CompareTo(numB);
        }
    }
}

In your original code, you attempted to use your MyComparer in Linq OrderBy as follows:

items = items.OrderByDescending(
  x => property.GetValue(x), comparer).ToList();

This approach is incorrect. The correct syntax for using your comparer is:

items = items.OrderBy(x => property.GetValue(x), comparer).ToList();

Note that the OrderBy method is used instead of OrderByDescending if you wish to sort in ascending order.

Finally, don't forget to assign the sorted items back to your data source to reflect the changes in your UI:

this.Items = items;

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