c# - foreach 语句给出错误

Question

我正在使用以下代码:

private string covertRss(string url)
    {
        var s = RssReader.Read(url);
        StringBuilder sb = new StringBuilder();
        foreach (RssNews rs in s)   //ERROR LINE
        {
            sb.AppendLine(rs.Title);
            sb.AppendLine(rs.PublicationDate);
            sb.AppendLine(rs.Description);
        }

        return sb.ToString();
    }

我收到一个错误:

Error 1 foreach statement cannot operate on variables of type 'System.Threading.Tasks.Task(System.Collections.Generic.List(Cricket.MainPage.RssNews))' because 'System.Threading.Tasks.Task(System.Collections.Generic.List(Cricket.MainPage.RssNews))' does not contain a public definition for 'GetEnumerator'

RssNews 类是:

public class RssNews
    {
        public string Title;
        public string PublicationDate;
        public string Description;

    }

我应该添加什么代码才能消除错误并且不影响代码的用途？ 提前致谢!

RssReader.Read() 代码

public class RssReader
    {
        public static async System.Threading.Tasks.Task<List<RssNews>> Read(string url)
        {
            HttpClient httpClient = new HttpClient();

            string result = await httpClient.GetStringAsync(url); 

            XDocument document = XDocument.Parse(result);

            return (from descendant in document.Descendants("item")
                    select new RssNews()
                    {
                        Description = descendant.Element("description").Value,
                        Title = descendant.Element("title").Value,
                        PublicationDate = descendant.Element("pubDate").Value
                    }).ToList();
        }
    }

Answer 1

你需要使用await:

foreach (RssNews rs in await s)

或:

var s = await RssReader.Read(url);

不使用Result；如果你这样做，你可以很容易地 cause a deadlock我在我的博客上描述的。

作为旁注，我建议您阅读并遵循 Task-based Asynchronous Pattern documentation 中的指南。 .如果这样做，您会发现您的方法 Read 应该命名为 ReadAsync，这会强烈提示您的调用代码需要使用 await:

var s = await RssReader.ReadAsync(url);