Static Methods in an Interface/Abstract Class

Asked 2008-08-18T13:42:08.530

First off, I understand the reasons why an interface or abstract class (in the .NET/C# terminology) cannot have abstract static methods. My question is then more focused on the best design solution.

What I want is a set of "helper" classes that all have their own static methods such that if I get objects A, B, and C from a third party vendor, I can have helper classes with methods such as

AHelper.RetrieveByID(string id);
AHelper.RetrieveByName(string name);
AHelper.DumpToDatabase();

Since my AHelper, BHelper, and CHelper classes will all basically have the same methods, it seems to makes sense to move these methods to an interface that these classes then derive from. However, wanting these methods to be static precludes me from having a generic interface or abstract class for all of them to derive from.

I could always make these methods non-static and then instantiate the objects first such as

AHelper a = new AHelper();
a.DumpToDatabase();

However, this code doesn't seem as intuitive to me. What are your suggestions? Should I abandon using an interface or abstract class altogether (the situation I'm in now) or can this possibly be refactored to accomplish the design I'm looking for?

Edit Report

3 Answers

For a generic solution to your example, you can do this:

public static T RetrieveByID<T>(string ID)
{
     var fieldNames = getFieldNamesBasedOnType(typeof(T));
     QueryResult qr = webservice.query("SELECT "+fieldNames + " FROM "
                                     + tyepof(T).Name
                                     +" WHERE Id = '" + ID + "'");
     return (T) qr.records[0];
}

answered 2008-08-18T14:30:03.053

In C# 3.0, static methods can be used on interfaces as if they were a part of them by using extension methods, as with DumpToDatabase() below:

static class HelperMethods
 {  //IHelper h = new HeleperA();
    //h.DumpToDatabase() 
    public static void DumpToDatabase(this IHelper helper) { /* ... */ }

    //IHelper h = a.RetrieveByID(5)
    public static IHelper RetrieveByID(this ObjectA a, int id) 
     { 
          return new HelperA(a.GetByID(id));
     }

    //Ihelper h = b.RetrieveByID(5)       
    public static IHelper RetrieveByID(this ObjectB b, int id)
     { 
          return new HelperB(b.GetById(id.ToString())); 
     }
 }

answered 2008-08-18T13:46:54.247

marxidad Just a quick point to note, Justin has already said that the SQL varies a lot dependant on the type, so I have worked on the basis that it could be something completely different dependant on the type, hence delegating it to the subclasses in question. Whereas your solution couples the SQL VERY tightly to the Type (i.e. it is the SQL).

rptony Good point on the possible sync issues with statics, one I failed to mention, so thank you :) Also, its Rob Cooper (not Copper) BTW ;) :D ( EDIT: Just thought I would mention that in case it wasn't a typo, I expect it is, so no problem!)

answered 2008-08-18T14:42:11.407

Static Methods in an Interface/Abstract Class

3 Answers

Your Answer