c# - 如何等到任务在 C# 中完成？

Question

我想向服务器发送请求并处理返回值:

private static string Send(int id)
{
    Task<HttpResponseMessage> responseTask = client.GetAsync("aaaaa");
    string result = string.Empty;
    responseTask.ContinueWith(x => result = Print(x));
    responseTask.Wait(); // it doesn't wait for the completion of the response task
    return result;
}

private static string Print(Task<HttpResponseMessage> httpTask)
{
    Task<string> task = httpTask.Result.Content.ReadAsStringAsync();
    string result = string.Empty;
    task.ContinueWith(t =>
    {
        Console.WriteLine("Result: " + t.Result);
        result = t.Result;
    });
    task.Wait();  // it does wait
    return result;
}

我是否正确使用了 Task？我不这么认为，因为 Send() 方法每次都返回 string.Empty，而 Print 返回正确的值。

我做错了什么？如何从服务器获得正确的结果？

Answer 1

您的 Print 方法可能需要等待继续完成(ContinueWith 返回一个您可以等待的任务)。否则第二个 ReadAsStringAsync 完成，该方法返回(在继续分配结果之前)。您的发送方法中存在同样的问题。两者都需要等待继续才能始终如一地获得您想要的结果。类似下面

private static string Send(int id)
{
    Task<HttpResponseMessage> responseTask = client.GetAsync("aaaaa");
    string result = string.Empty;
    Task continuation = responseTask.ContinueWith(x => result = Print(x));
    continuation.Wait();
    return result;
}

private static string Print(Task<HttpResponseMessage> httpTask)
{
    Task<string> task = httpTask.Result.Content.ReadAsStringAsync();
    string result = string.Empty;
    Task continuation = task.ContinueWith(t =>
    {
        Console.WriteLine("Result: " + t.Result);
        result = t.Result;
    });
    continuation.Wait();  
    return result;
}