yield在WCF中的错误使用——99%的开发人员都有可能犯的错误[下篇]

static void Main(string[] args)
{
    IEnumerable<string> items = GetItems();
    Console.WriteLine("Begin to iterate the collection.");
    items.ToArray();
}

static IEnumerable<string> GetItems()
{
    Console.WriteLine("Begin to invoke GetItems() method");
    yield return "Foo";
    yield return "Bar";
    yield return "Baz";
}

Begin to invoke GetItems() method
Begin to iterate the collection.

Begin to iterate the collection.
Begin to invoke GetItems() method

internal class Program
{
    private static IEnumerable<string> GetItems()
    {
        return new <GetItems>d__0(-2);
    }
    private sealed class <GetItems>d__0 : IEnumerable<string>, IEnumerable, IEnumerator<string>, IEnumerator, IDisposable
}

private sealed class <GetItems>d__0 : IEnumerable<string>, IEnumerable, IEnumerator<string>, IEnumerator, IDisposable
{
    private int <>1__state;
    private string <>2__current;

    private bool MoveNext()
    {
        switch (this.<>1__state)
        {
            case 0:
                this.<>1__state = -1;
                Console.WriteLine("Begin to invoke GetItems() method");
                this.<>2__current = "Foo";
                this.<>1__state = 1;
                return true;

            case 1:
                this.<>1__state = -1;
                this.<>2__current = "Bar";
                this.<>1__state = 2;
                return true;

            case 2:
                this.<>1__state = -1;
                this.<>2__current = "Baz";
                this.<>1__state = 3;
                return true;

            case 3:
                this.<>1__state = -1;
                break;
        }
        return false;
    }
    string IEnumerator<string>.Current
    {
        [DebuggerHidden]
        get
        {
            return this.<>2__current;
        }
    }

    object IEnumerator.Current
    {
        [DebuggerHidden]
        get
        {
            return this.<>2__current;
        }
    }
}

public class DemoService : IDemoService
{
    public IEnumerable<string> GetItems(string categoty)
    {
        if (string.IsNullOrEmpty(categoty))
        {
            throw new FaultException("Invalid category");
        }
        yield return "Foo";
        yield return "Bar";
        yield return "Baz";
    }
}

public class DemoService : IDemoService
{
    public IEnumerable<string> GetItems(string categoty)
    {
        if (string.IsNullOrEmpty(categoty))
        {
            throw new FaultException("Invalid category");
        }
        return new string[] { "Foo", "Bar", "Baz" };
    }
}