将WebClient方法转换为async / await

时间:2012-11-05 21:45:56

标签: c# microsoft-metro async-await

我有一些现有的代码,我移植到Windows 8 WinRT。代码从URL获取数据,异步调用传递的委托:

private void RequestData(string uri, Action<string> action)
{
  var client = new WebClient();
  client.DownloadStringCompleted += (s,e) => action(e.Result);
  client.DownloadStringAsync(new Uri(uri));
}

转换为WinRT需要使用HttpClient和异步方法。我已经阅读了一些关于async / await的教程,但有点困惑。如何更改上述方法,但保留方法签名以避免更改我的代码?

6 个答案:

答案 0 :(得分:79)

private async void RequestData(string uri, Action<string> action)
{
    var client = new WebClient();
    string data = await client.DownloadStringTaskAsync(uri);
    action(data);
}

请参阅:http://msdn.microsoft.com/en-us/library/hh194294.aspx

答案 1 :(得分:9)

  

如何更改上述方法,但保留方法签名以避免更改我的代码?

最好的答案是“你没有”。如果您使用async,请将其一直使用。

private async Task<string> RequestData(string uri)
{
  using (var client = new HttpClient())
  {
    return await client.GetStringAsync(uri);
  }
}

答案 2 :(得分:6)

关注this example,首先使用await创建异步任务,然后使用Task<string> downloadStringTask = client.DownloadStringTaskAsync(new Uri(uri)); string result = await downloadStringTask; 获取结果:

{{1}}

答案 3 :(得分:4)

var client = new WebClient();
string page = await client.DownloadStringTaskAsync("url");

var client = new HttpClient();
string page = await client.GetStringAsync("url");

答案 4 :(得分:3)

await HttpClient.GetStringAsync Method

的结果
var client = new HttpClient();
action(await client.GetStringAsync(uri));

答案 5 :(得分:-1)

这段代码是针对UploadValuesAsync的:

public class WebClientAdvanced : WebClient
{
    public async Task<byte[]> UploadValuesAsync(string address, string method, IDictionary<string, string> data)
    {
        var nvc = new NameValueCollection();
        foreach (var x in data) nvc.Add(x.Key, x.Value.ToStr());

        var tcs = new TaskCompletionSource<byte[]>();
        UploadValuesCompleted += (s, e) =>
        {
            if (e.Cancelled) tcs.SetCanceled();
            else if (e.Error != null) tcs.SetException(e.Error);
            else tcs.SetResult(e.Result);
        };

        UploadValuesAsync(new Uri(address), method, nvc);
        var result = await tcs.Task;
        return result;
    }
}