Question

I want to write a custom comparer for a SortedDictionary, where keys are sorted based on their type. Is this possible?

public class StateBase
{
    // This is a base class I have to inherit from
}

SortedDictionary<StateBase, int> _stateDictionary =
    new SortedDictionary<StateBase, int>(new StateComparer());

class StateComparer : IComparer<StateBase>
{
    public int Compare(StateBase a, StateBase b)
    {
        // I'd like to sort these based on their type
        // I don't particularly care what order they are in, I just want them
        // to be sorted.
    }
}

Answer 1

You can. If your comparer implements IComparer<T>, it can be passed to a new SortedDictionary instance by the corresponding constructor overload.

The Compare method then somehow decides what item is greater or lower. It is the place where you can implement your compare-by-type logic.

Here is an example to compare Type instances based on their name:

public class TypeComparer : IComparer<Type>
{
    public int Compare(Type x, Type y)
    {
        if(x != null && y != null)
            return x.FullName.CompareTo(y.FullName);
        else if(x != null)
            return x.FullName.CompareTo(null);
        else if(y != null)
            return y.FullName.CompareTo(null);
        else
            return 0;
    }
}