I'm implementing a factory pattern that looks as follows.
public class FeedFactory
{
#region Singleton Pattern
//..
#endregion
private static Feed[] _factory = new Feed[(int)FeedType.Total];
public void RegisterFeed(FeedType feedType,Feed feed)
{
if (_factory[(int)feedType] == null)
{
_factory[(int)feedType] = feed;
}
else
{
// already registered
}
}
public Feed GetFeed(FeedType feedType)
{
return _factory[(int)feedType];
}
}
Here, Feed
is an abstract class from which the different classes inherit. How can I register the different classes? Is it possible to do it from their constructor?
This is not a factory pattern. A factory will always have some constructor logic in it, at least one new
. That's the idea of a factory: the caller doesn't have to worry about how objects are created. This is a singleton repository.
So first of all, instead of using an array, you should be having a type indexed dictionary.
private static Dictionary<Type, Feed> _singletons = new Dictionary<Type, Feed>();
After that, you don't need a register method. The dictionary should be filled automatically when you retrieve singletons.
Now I suppose your Feed class has a default constructor without arguments. In that case, you can implement a factory method directly from the abstract class Feed. We're going to use some generics here, because it allows you to control inheritance:
public abstract class Feed
{
public static T GetInstance<T>() where T:Feed, new()
{
T instance = new T();
// TODO: Implement here other initializing behaviour
return instance;
}
}
Now back to your singleton repository.
public class FeedSingletonRepository
{
private static readonly object _padlock = new object();
private static Dictionary<Type, Feed> _singletons = new Dictionary<Type, Feed>();
public static T GetFeed<T>() where T:Feed
{
lock(_padlock)
{
if (!_singletons.ContainsKey(typeof(T))
{
_singletons[typeof(T)] = Feed.GetInstance<T>();
}
return (T)_singletons[typeof(T)];
}
}
}
Note that I included a threadsafe behaviour which is a good thing to do when you work with singletons.
Now if you want to get the singleton for a given type inheriting from Feed
(let's call it SpecializedFeedType
), all you have to do is:
var singleton = FeedSingletonRepository.GetFeed<SpecializedFeedType>();
or
SpecializedFeedType singleton = FeedSingletonRepository.GetFeed();
which is the same line with a slightly different syntax.
Edit2: changed some syntax errors.
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