Easiest way to get a common base class from a collection of types

Question

I\'m building a custom property grid that displays the properties of items in a collection. What I want to do is show only the properties in the grid that are common amongst

Answer 1

I use something like this but Tony's answer is probably better:

internal class BaseFinder
{
    public static Type FindBase(params Type[] types)
    {
        if (types == null)
            return null;

        if (types.Length == 0)
            return null;

        Dictionary> baseTypeMap = new Dictionary>();

        // get all the base types and note the one with the longest base tree
        int maxBaseCount = 0;
        Type typeWithLongestBaseTree = null;
        foreach (Type type in types)
        {
            IList baseTypes = GetBaseTree(type);
            if (baseTypes.Count > maxBaseCount)
            {
                typeWithLongestBaseTree = type;
                maxBaseCount = baseTypes.Count;
            }
            baseTypeMap.Add(type, baseTypes);
        }

        // walk down the tree until we get to a common base type
        IList longestBaseTree = baseTypeMap[typeWithLongestBaseTree];
        for (int baseIndex = 0; baseIndex < longestBaseTree.Count;baseIndex++)
        {
            int commonBaseCount = 0;
            foreach (Type type in types)
            {
                IList baseTypes = baseTypeMap[type];
                if (!baseTypes.Contains(longestBaseTree[baseIndex]))
                    break;
                commonBaseCount++;
            }
            if (commonBaseCount == types.Length)
                return longestBaseTree[baseIndex];
        }
        return null;
    }

    private static IList GetBaseTree(Type type)
    {
        List result = new List();
        Type baseType = type.BaseType;
        do
        {
            result.Add(baseType);
            baseType = baseType.BaseType;
        } while (baseType != typeof(object));
        return result;
    }
}