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copied!<p>If I understood you correctly, you have an interface that provides multiple methods, each of which takes basically the same kind of delegate, but gets a different type of parameter as input. Something like this:</p> <pre><code>GetListOfSongs(..., delegate(List<Song> result) { ... }); GetListOfMovies(..., delegate(List<Movie> result) { ... }); </code></pre> <p>and you're worried about the delegate signatures that start cropping up along with the methods in the interface?</p> <p>If that's the case, then generics are what you're looking for. In fact, if your delegate signature matches my example -- that is, accepts one input parameter, returns no value -- the delegate type you want already exists in the BCL. It's called <code>Action<T></code>. You could declare the methods above like so:</p> <pre><code>GetListOfSongs(..., Action<List<Song>> callback); GetListOfMovies(..., Action<List<Movie>> callback); </code></pre> <p>and you'd still only have a single delegate type, that is, <code>Action<T></code>.</p> <p>Now, if you need to pass along more than one parameter, you're still covered. There exist versions of Action for up to 16 input parameters (although their signatures begin to look a bit garish: <code>Action<T1, T2, T3 ...></code>).</p> <p>If you want your callback to also return a value that you'll use somewhere within your infrastructure, <code>Func<T, TResult></code> is your friend (T is the type of the input parameter, TResult is the type of the value you will return from the delegate).</p> <p>As a bonus, I'd recommend you don't expose <code>List<T></code> in your interfaces. If you really think all your clients will need list operations, use <code>IList<T></code>, but consider <code>ICollection<T></code> or even <code>IEnumerable<T></code> if they won't.</p>

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