为异步方法返回列表的最佳方式是什么?

我正在使用此示例编写RSS阅读器 https://github.com/dotnet/SyndicationFeedReaderWriter

我想记录所有 ISyndicationItem 的以列表形式返回。我得到的编译器错误是“error CS1983 async 方法必须为 void , Task , Task<T> ,类任务类型, IAsyncEnumerable<T> 或 IAsyncEnumerator<T> “最理想的方法是什么?

using Microsoft.SyndicationFeed;
using Microsoft.SyndicationFeed.Rss;
using System.Collections.Generic;
using System.Xml;

static async List<ISyndicationItem> ReadRSSFeed(string inputUri)
{
    var itemList = new List<ISyndicationItem>();
    using (var xmlReader = XmlReader.Create(inputUri,
        new XmlReaderSettings() { Async = true }))
    {
        var feedReader = new RssFeedReader(xmlReader);

        while (await feedReader.Read())
        {
            switch (feedReader.ElementType)
            {
                // Read category
                case SyndicationElementType.Category:
                    ISyndicationCategory category = await feedReader.ReadCategory();
                    break;

                // Read Image
                case SyndicationElementType.Image:
                    ISyndicationImage image = await feedReader.ReadImage();
                    break;

                // Read Item
                case SyndicationElementType.Item:
                    ISyndicationItem item = await feedReader.ReadItem();
                    itemList.Add(item);
                    break;

                // Read link
                case SyndicationElementType.Link:
                    ISyndicationLink link = await feedReader.ReadLink();
                    break;

                // Read Person
                case SyndicationElementType.Person:
                    ISyndicationPerson person = await feedReader.ReadPerson();
                    break;

                // Read content
                default:
                    ISyndicationContent content = await feedReader.ReadContent();
                    break;
            }
        }
    }
    return itemList;
}