using System;

 private static Comparer<TestcaseViewModel> bandsCountComparer = Comparer<TestcaseViewModel>.Create(

            (a, b) => a.ContestTestcase.GetExtension<ITestcasePropertyAccess>().GetPropertyValue("BandNumbers")

            .CompareTo(b.ContestTestcase.GetExtension<ITestcasePropertyAccess>().GetPropertyValue("BandNumbers")));