Refactoring group of yeild return statments to a method

Question

How would I go about grouping multiple yield statements to a method ?

I have the following code :

public IEnumerable<IPublisher> RegisterEvents()
{
    var url= Settings.wcfUrl;
    var publisher = PublisherFactory.Create<IWcfPublisher> (url)
        publisher.Register(new object(..));
        publisher.Register(new object(..));
     yield return publisher;

    var url = Settings.webpublisherurl;
    var publisher = PublisherFactory.Create<IWebPublisher> (url)
        publisher.Register(new object(..));
        publisher.Register(new object(..));
     yield return publisher;

    var url = Settings.webpublisherurl2;
    var publisher = PublisherFactory.Create<IWebPublisher2> (url)
        publisher.Register(new object(..));
        publisher.Register(new object(..));
     yield return publisher;
     . . .
}

The code is getting very large and I wanted to refactor some of the publishers to a static class EventHelper

public IEnumerable<IPublisher> RegisterEvents()
{
    var url= Settings.wcfUrl;
    var publisher = PublisherFactory.Create<IWcfPublisher> (url)
        publisher.Register(new object(..));
        publisher.Register(new object(..));
     yield return publisher;

    return yield EventHelper.CreateWebApiPublisher() //<-- compiler error
     . . .
}

CreateWebApiPublisher() looks like

public static IEnumerable<IPublisher> CreateWebApiPublisher()
{
    var url = Settings.webpublisherurl;
    var publisher = PublisherFactory.Create<IWebPublisher>(url)
    publisher.Register(new object(..));
    publisher.Register(new object(..));
    yield return publisher;

    var url = Settings.webpublisherurl2;
    var publisher = PublisherFactory.Create<IWebPublisher2>(url)
    publisher.Register(new object(..));
    publisher.Register(new object(..));
    yield return publisher;
}

I am confused how to use EventHelper.CreateWebApiPublisher() in RegisterEvents() I keep getting compiler error :

Error CS0266 Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<IPublisher>' to 'IPublisher'...

Answer 1

yield return can only yield a single value at a time. At the line where you're getting the compiler error, you need to iterate through the results of the method instead, and yield return them sequentially.

foreach (var p in EventHelper.CreateWebApiPublisher())
    yield return p;