Generic IComparer for sorting different objects in different properties

Question

I'm trying to sort an array of objects with IComparer.

I wrote the code but it works only with the particular object. e.g.:

for this class

public class Cars
{
    public string Name { get; set; }
    public string Manufacturer { get; set; }
    public int Year { get; set; }

    public Cars(string name, string manufacturer, int year)
    {
        Name = name;
        Manufacturer = manufacturer;
        Year = year;
    }
}

My code looks like:

class MySort 
{
    public class SortByYears : IComparer
    {
        int IComparer.Compare(Object x, Object y)
        {
            Cars X = (Cars)x, Y = (Cars)y;                
            return (X.Year.CompareTo(Y.Year));
        }
    }

    public class SortByName : IComparer
    {
        int IComparer.Compare(Object x, object y)
        {
            Cars X = (Cars)x, Y = (Cars)y;
            return (X.Name.CompareTo(Y.Name));
        }
    }

    public class SortByManyfacturer : IComparer
    {
        int IComparer.Compare(object x, object y)
        {
            Cars X = (Cars)x, Y = (Cars)y;
            return (X.Manufacturer.CompareTo(Y.Manufacturer));
        }
    }
}   

But if I add another class with different properties it will be useless.

So is there any chance to modify this code so that it worked for objects with different properties?

Answer 1

class SortComparer<T> : IComparer<T>
{
   private PropertyDescriptor PropDesc = null;
   private ListSortDirection Direction =
      ListSortDirection.Ascending;

   public SortComparer(object item,string property,ListSortDirection direction)
   {
       PropDesc = TypeDescriptor.GetProperties(item)[property];
       Direction = direction;
   }

   int IComparer<T>.Compare(T x, T y)
   {    
      object xValue = PropDesc.GetValue(x);
      object yValue = PropDesc.GetValue(y);
      return CompareValues(xValue, yValue, Direction);
   }

   private int CompareValues(object xValue, object yValue,ListSortDirection direction)
   {

      int retValue = 0;
      if (xValue is IComparable) // Can ask the x value
      {
         retValue = ((IComparable)xValue).CompareTo(yValue);
      }
      else if (yValue is IComparable) //Can ask the y value
      {
         retValue = ((IComparable)yValue).CompareTo(xValue);
      }
      // not comparable, compare String representations
      else if (!xValue.Equals(yValue))
      {
         retValue = xValue.ToString().CompareTo(yValue.ToString());
      }
      if (direction == ListSortDirection.Ascending)
      {
         return retValue;
      }
      else
      {
         return retValue * -1;
      }
   }
}

Calling code:

Assuming a list named lst:

lst.Sort(new SortComparer<Cars>(lst[0],"YourPropertyName",ListSortDirection.Ascending));

Answer 2

You may leverage the Create method of Comparer<T> which takes a Comparison delegate and returns Comparer<T>.

var carnameComparer = Comparer<Cars>.Create((x, y) => x.Year.CompareTo(y.Year));
var carManufacturerComparer = Comparer<Cars>.Create((x, y) => x.Manufacturer.CompareTo(y.Manufacturer));

and for another type

var carsComparer = Comparer<SomeType>.Create((x, y) => x.SomeProperty.CompareTo(y.SomeProperty));

If you're in prior to .Net4.5 you can use the following CreateComparer method.

private static IComparer<T> CreateComparer<T>(Comparison<T> comparison)
{
    return new ComparisonComparer<T>(comparison);
}

public class ComparisonComparer<T> : IComparer<T>
{
    private Comparison<T> comparison;
    public ComparisonComparer(Comparison<T> comparison)
    {
        if (comparison == null)
        {
            throw new ArgumentNullException("comparison");
        }
        this.comparison = comparison;
    }

    public int Compare(T x, T y)
    {
        return comparison(x, y);
    }
}