Question

I am not able to find out as to how to implement the IComparable interface method CompareTo for a generic class.

I have a class called BindingProperty<T> which is used to create a List<BindingProperty<intOrString>> to bind to a DataGrid. The problem is that the I can not perform the Sort operation as the IComparable interface is not implemented by this BindingProperty<T> class. The result of comparison would depend on a data member ‘Value’ of the the BindingProperty<T> class where ‘Value’ is of Type T. When I click on the column header of the DataGrid, I get an exception that CompareTo() method is not implemented.

I would need help to implement this interface. Should I be using IComparable<T>? If yes, how do I do it?

Thanks in advance
Shakti

Answer 1

Set up a generic type constraint on T.

public class BindingProperty<T> : IComparable where T : IComparable
{
    public T Value {get; set;}

    public int CompareTo(object obj)
    {
       if (obj == null) return 1;

       var other = obj as BindingProperty<T>;
       if (other != null) 
            return Value.CompareTo(other.Value);
       else
            throw new ArgumentException("Object is not a BindingProperty<T>");
    }
}

Edit:
Alternative solution to handle if value does not implement IComparable. This will support all types, just wont sort if they do not implement IComparable.

public class BindingProperty<T> : IComparable
    {
        public T Value {get; set;}

        public int CompareTo(object obj)
        {
           if (obj == null) return 1;

           var other = obj as BindingProperty<T>;
           if (other != null) 
           {
               var other2 = other as IComparable;
               if(other2 != null)
                  return other2.CompareTo(Value);
               else
                  return 1; //Does not implement IComparable, always return 1
           }
           else
                throw new ArgumentException("Object is not a BindingProperty<T>");
        }
    }