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

The code posted to get the most-specific common base for a set of types has some issues. In particular, it breaks when I pass typeof(object) as one of the types. I believe the following is simpler and (better) correct.

public static Type GetCommonBaseClass (params Type[] types)
{
    if (types.Length == 0)
        return typeof(object);

    Type ret = types[0];

    for (int i = 1; i < types.Length; ++i)
    {
        if (types[i].IsAssignableFrom(ret))
            ret = types[i];
        else
        {
            // This will always terminate when ret == typeof(object)
            while (!ret.IsAssignableFrom(types[i]))
                ret = ret.BaseType;
        }
    }

    return ret;
}

I also tested with:

Type t = GetCommonBaseClass(typeof(OleDbCommand),
                            typeof(OdbcCommand),
                            typeof(SqlCommand));

And got typeof(DbCommand). And with:

Type t = GetCommonBaseClass(typeof(OleDbCommand),
                            typeof(OdbcCommand),
                            typeof(SqlCommand),
                            typeof(Component));

And got typeof(Compoment). And with:

Type t = GetCommonBaseClass(typeof(OleDbCommand),
                            typeof(OdbcCommand),
                            typeof(SqlCommand),
                            typeof(Component),
                            typeof(Component).BaseType);

And got typeof(MarshalByRefObject). And with

Type t = GetCommonBaseClass(typeof(OleDbCommand),
                            typeof(OdbcCommand),
                            typeof(SqlCommand),
                            typeof(Component),
                            typeof(Component).BaseType,
                            typeof(int));

And got typeof(object).