Question

I need to convert a VB Collection to a modern one, like Dictionary or Hashtable. For my approach, I need the Collection’s KEYS. Googling tells me that it’s impossible.

Re-writing the entire application using new collections is not an option as the application is really old and large (converted from VB6 to VB.Net).
Using the old Collection also is not good – as there are new components in development.

Converting a – for example – Hashtable to Collection works:

 using VBCollection = Microsoft.VisualBasic.Collection;
 public static VBCollection ToVBCollection(this Hashtable table)
    {
        var collection = new VBCollection();
        foreach (DictionaryEntry  pair in table)
        {
            collection.Add(pair.Value, pair.Key as string);
        }
        return collection;
    }

Converting a VBCollection does not, because I don’t know how to retrieve the key:

 using VBCollection = Microsoft.VisualBasic.Collection;
  public static Hashtable ToHashtable(this VBCollection Collection)
    {
        var table = new Hashtable();

        foreach (var pair in Collection)
        {
            table.Add(pair.Key, pair.Value); //I need the key and the corresponding value
        }
        return table;
    }

Any advices? If retrieving the key really is impossible (Thanks, Microsoft), then how should I convert a VB COllection to something modern?

Thanks in advance

Answer 1

If it is a requirement to have as little impact on your existing codebase as possible, I’d write a drop-in replacement for the Collection. It would be easy (if not a little tedious) to write your own class that exposed all of the same methods as the VB Collection but alos included additional methods to return the keys. You could either inherit from some of the built-in .NET collection types or just use compisition to wrap a Hashtable. You can then change your Imports clauses in your converted VB.NET application to include your Collection intsead of the Microsoft.VisualBasic.Collection.

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For the heck of it, I’ll post an alternate, but more complicated solution. You can use Reflection to get the private Dictionary that the VB Collection object uses internally. With that you could iterate the keys. This is more of a hack than the other approach, but should work equally well. One caveat is that accessing the private members of a class is prone to being broken if MS changes the internals of the class.