Passing property as parameter in method

Question

I know the title could probably be a bit more descriptive/better phrased, but it was the best I could come up with.

Currently I have a class with a lot of methods looking like the ones below:

        private static void UpdateArtists()
        {
            artists.Clear();
            foreach (AudioInfo entry in library_entries)
            {
                artists.Add(entry.Artist, entry);
            }
        }

        private static void UpdateAlbums()
        {
            albums.Clear();
            foreach (AudioInfo entry in library_entries)
            {
                albums.Add(entry.Album, entry);
            }
        }

        private static void UpdateGenres()
        {
            genres.Clear();
            foreach (AudioInfo entry in library_entries)
            {
                genres.Add(entry.Genre, entry);
            }
        }

        private static void UpdateYears()
        {
            years.Clear();
            foreach (AudioInfo entry in library_entries)
            {
                years.Add(entry.Year, entry);
            }
        }

Needless to say, writing dozens of these is very tiresome. So I was wondering if it's possible to simplify it and make a method something like this:

     private static void Update(Dictionary<string, AudioInfo> dictionary, AudioInfo.Property property)
     {
         dictionary.Clear();
         foreach (AudioInfo entry in library_entries)
         {
             dictionary.Add(entry.property, entry);
         }
         //Where "property" is a property in the AudioInfo-class.
     }

Is that doable, and if it is; how?

Thanks!

Note that you don't need `ref` at all, classes are always passed by reference. — Julien Lebosquain, Jul 10 '11 at 09:39
Heh, you're right of course. That's what you get when you sit up the entire night. — Heidenreich, Jul 10 '11 at 09:42
possible duplicate of [How can I pass a property of a class as a parameter of a method?](http://stackoverflow.com/questions/1178574/how-can-i-pass-a-property-of-a-class-as-a-parameter-of-a-method) — nawfal, Feb 11 '13 at 10:38

oxilumin · Answer 1 · 2011-07-10T09:53:51.990

15

It seems like you have some design errors in your class if you need to do such things. nevertheless, the solution is:

private static void Update(Dictionary<string, AudioInfo> dictionary, Func<AudioInfo, string> func)
{
    dictionary.Clear();
    foreach (AudioInfo entry in library_entries)
    {
        dictionary.Add(func(entry), entry);
    }
}

And the usage is:

Update(years, x => x.Year);

Also you can use easier way, instead of call any methods you can just write:

years = library_entries.ToDictionary(x => x.Year, x => x);

If you have not any events, linked with your dictionary.

And one more thing to go - you can't add different elements with the same keys to dictionary. In your case it seems like you have different AudioInfo objects with the same Year, Genre e.t.c.

edited Jul 10 '11 at 09:53

answered Jul 10 '11 at 09:37

oxilumin

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You don't have to pass dictionary by `ref`. – Jalal Said Jul 10 '11 at 09:42
Yes, you are right, I just copied the signature from the question. – oxilumin Jul 10 '11 at 09:59
Actually I have a custom OneToManyDictionary, that has a list of items for each key. If I add a duplicate key, it adds the value to the list associated with the key. Thought I'd simplify my question and just use a regular Dictionary to avoid more confusion than needed :d. That being said, guess I'll go with the Func version. Thanks! – Heidenreich Jul 10 '11 at 10:07
I'm genuinely curious what the design errors are in this case. My code could really benefit from such a critique. What are the errors and how could they be fixed? – kdbanman Aug 19 '15 at 19:07

Passing property as parameter in method

1 Answers1

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