How to replace enumeration with something like interface ID?

Question

Please consider the following interfaces:

interface IFile
{
    // Members
};

interface IAudioFile : IFile
{
    // Members
};

interface IVideoFile : IFile
{
    // Members  
};

enum ContentType
{
    Audio,
    Video
};

interface IProvider
{
    HashSet<ContentType> GetSupportedTypes();
    IList<IFile> GetFiles(ContentType contentType);
};

I think that ContentType enumeration is redundant. Is there any way to use something like interface identifier instead of enumeration type?

Any comments on the interface design are very appreciated.

@Abdul, just because interface type maps to the enumeration value: IAudioFile => ContentType.Audio; IVideoFile => ContentType.Video — Sergey Vyacheslavovich Brunov, May 16 '11 at 11:00

score 3 · Accepted Answer · answered May 16 '11 at 10:57

3

It really depends on what you're trying to accomplish, but I one options you may want to look at is using generics, so that IProvider is as so

interface IProvider
{
    IList<IFile> GetFiles<T>() where T: IFile;
}

which can be implemented like so

public void ProviderConcrete()
{
    public IList<IFile> GetFiles<T>()
    {
        if(typeof(t) == typeof(IAudioFile))
            .... get Audio files

    }
}

and called like so

public void Caller()
{
    var files = GetFiles<IAudioFile>();
}

answered May 16 '11 at 10:57

Jaimal Chohan

8,530
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Ok, nice! But how about getting information about supported file types (see GetSupportedTypes)? – Sergey Vyacheslavovich Brunov May 16 '11 at 11:02
Hmm, in what scenario would you need to call GetSupportedTypes? – Jaimal Chohan May 16 '11 at 12:23
Clients should have a possibility to get a set of supported types and then get only supported types one by one. – Sergey Vyacheslavovich Brunov May 16 '11 at 12:34
You could hardcode this method to return a list of types, but then you'd probably forget to update it one day and boom. The other option would be to use reflection to iterate over all the types in your assembly and pick out the ones that implement IFile – Jaimal Chohan May 16 '11 at 12:43
iteration over all the types in assembly is the best practice for solving such a problem? – Sergey Vyacheslavovich Brunov May 17 '11 at 04:44

score 0 · Answer 2 · answered May 16 '11 at 10:58

Usually, it's better to write something like this:

void method(IFile file) {
    file.DoYourThing();
}

than

void method(ContentType id) {
   switch (id) {
   case ContentType.Audio: 
       file.DoThis();
       break;

   case ContentType.Video: 
       file.DoThat();
       break;
   }
}

That's because switches usually become a maintenance nightmare as time passes by, and it's error prone too.

My recommendation is that when you need switches or if-else chains you should consider to insert a method to an already existing class hierarchy or to create a new one. You should strive to write code that look like the one you see in the first code snippet.

As usual, this is generic so it may not apply to your particular problem at hand.

score 0 · Answer 3 · answered May 16 '11 at 10:59

0

I think that the point here is that the returned list contains "base" objects.

If you don't like that, you could create some overloads like

IList<IAudioFile> GetAudioFiles();
IList<IVideoFile> GetVideoFiles();

answered May 16 '11 at 10:59

Paolo Tedesco

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Sorry, but I have not mentioned that the files' class hierarchy will probably grow later. So, I need more flexible mechanism. – Sergey Vyacheslavovich Brunov May 16 '11 at 11:05

How to replace enumeration with something like interface ID?

3 Answers3