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User12351259599491
Asked:2020-01-25 04:44:06 +0000 UTC2020-01-25 04:44:06 +0000 UTC

如何将异步方法的返回值转换为 List<string>？

  • 772

有一个类有一个方法：

class ParsGoogle
{


    public static async Task<List<string>> ParsUrlAsync(string url)
    {
        var requester = new DefaultHttpRequester();

        requester.Headers["User-Agent"] = "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:68.0) Gecko/20100101 Firefox/68.0";
        var config = Configuration.Default.With(requester).WithDefaultLoader().WithJs();
        var context = BrowsingContext.New(config);
        var address = "https://www.google.com/search?q=" + url;
        AngleSharp.Dom.IDocument documentGoogle;  
        documentGoogle = await context.OpenAsync(address);           
        var elements = documentGoogle.QuerySelectorAll("div.g>div:nth-child(1)>div:nth-child(1)>div:nth-child(1)>a:nth-child(1)").Attr("href");

        return elements;// тут ошибка Не удается неявно преобразовать тип "System.Collections.Generic.IEnumerable<string>" в "System.Collections.Generic.List<string>". Существует явное преобразование (возможно, пропущено приведение типов).

    }
}

如果return (System.Collections.Generic.List<string>)elements;在方法中显式指定 To 类型的转换，则会发生异常 System.InvalidCastException ：我这样运行它：

static async Task Main(string[] args)
{
    List<string> url = new List<string>();
    List<string> proxy = new List<string>();
    List<string> list = new List<string>();
    using (StreamReader temp = new StreamReader(@"c:\Users\root\Desktop\proxy.txt"))
    {
        while (temp.Peek() != -1)
        {
            list.Add(temp.ReadLine());
        }


        await Task.Run(async () =>
        {
            list = await ParsGoogle.ParsUrlAsync(list.First());

        });
        

    }
    foreach (string i in list) 
    {
        Console.WriteLine(i);
    }
    Console.ReadLine();
}

问题是如何正确转换类型？或者如何解决？

c#

1 个回答

  1. Best Answer
    public static async Task<IEnumerable<string>> ParsUrlAsync(string url)
{
  ...
}

List<string> list = new List<string>();
IEnumerable<string> result = null;
using (StreamReader temp = new StreamReader(@"c:\Users\root\Desktop\proxy.txt"))
{
  ...
  result = await ParsGoogle.ParsUrlAsync(list.First());
  ...
}

foreach (string i in result) 
{
  Console.WriteLine(i);
}
    • 2

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