如何正确地将HttpClient与async/await一起使用? [英] How do I correctly use HttpClient with async/await?

问题描述

以下代码出现两个错误:

I'm getting two errors for the following code:

public async Task<string> TestDownloadTask()
{
    HttpResponseMessage response = null;

    using (HttpClient client = new HttpClient())
    {
        client.BaseAddress = new Uri(@"https://api.nasa.gov/planetary/apod");
        client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

        response.EnsureSuccessStatusCode();
        response = await client.GetStringAsync("?concept_tags=True&api_key=DEMO_KEY");
    }

    return response.Content;
}

我得到了:

• 无法在等待"行上等待"System.Threading.Tasks.Task"
• 无法将表达式类型'System.Net.Http.Content'转换为返回类型'string'

我一直在尝试编写上面的代码，这些代码将从Web服务下载一个字符串，但是关于如何使用async和await和如何使用HttpClient似乎有很多相互矛盾的信息，我不知道我编写的代码有什么问题.

I've been attempting to write the above code that will download a string from a web service, but there seems to be a lot of conflicting information about how to use async and await and how to use HttpClient and I do not know what is wrong with the code I've written.

我要去哪里错了，应该怎么做呢?

Where am I going wrong and how should I be doing it instead?

推荐答案

此方法client.GetStringAsync返回Task<string>

public Task<string> TestDownloadTask()
{
    using (HttpClient client = new HttpClient())
    {
        client.BaseAddress = new Uri(@"https://api.nasa.gov/planetary/apod");
        client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

        // You don't need await here
        return client.GetStringAsync("?concept_tags=True&api_key=DEMO_KEY");
    }
}

要使用上述功能:

public async void SomeMethod()
{
    // await to get string content
    string mystring = await TestDownloadTask();
}

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