异步等待Windows Phone Web访问API

Question

Is there support for the async/await pattern in WP8?

I need to get XML from a web-based API and it looks like that WebClient or WebRequest do not support it.

Are there classes that support async/await usable for web access in the WP8 BCL? And if not, is there a library I can use?

I know it is not that hard to create wrappers to support it, but this seems like a thing that would be included in the SDK.

Answer 1

Are there classes that support async/await usable for web access in the WP8 BCL?

This is a concern that has been raised during the closed beta of the WP8 SDK, so I can answer that unfortunately, no.

But as you mentioned, it is reasonably easy to make your own wrappers.

For instance:

public static class Extensions
{
    public static Task<string> DownloadStringTask(this WebClient webClient, Uri uri)
    {
        var tcs = new TaskCompletionSource<string>();

        webClient.DownloadStringCompleted += (s, e) =>
        {
            if (e.Error != null)
            {
                tcs.SetException(e.Error);
            }
            else
            {
                tcs.SetResult(e.Result);
            }
        };

        webClient.DownloadStringAsync(uri);

        return tcs.Task;
    }
}

Answer 2

There is some support for WP8 in the Microsoft.Threading.Tasks.Extensions.Phone.dll provided as part of the Microsoft.Bcl.Async NuGet package described in this blog post .

In particular, it includes WebClient.DownloadStringTaskAsync .

Answer 3

I had the same issue and I found this and helped me

private async Task<T> ExecuteAsync<T>(RestRequest request)
    {
        var tcs = new TaskCompletionSource<T>();
        _client.ExecuteAsync(request, resp =>
        {
            var value = JsonConvert.DeserializeObject<T>(resp.Content);
            if (value.ErrorCode > 0)
            {
                var ex = new ToodledoException(value.ErrorCode, value.ErrorDesc);
                tcs.SetException(ex);
            }
            else
                tcs.SetResult(value);
        });
        return await tcs.Task;
    }

http://www.developer.nokia.com/Community/Wiki/Asynchronous_Programming_For_Windows_Phone_8 also I found this extension helpful http://nuget.org/packages/WP8AsyncWebClient/

Answer 4

Is there support for the async/await pattern in WP8?

Just to clarify, there is full C# 5.0 support on Windows Phone 8. The WinRT APIs largely depend on async/await, such as syncing to PeopleHub, or using the I/O APIs.

But the Silverlight and old .NET APIs have not been updated to use async/await for classes like the WebClient.

Answer 5

WP8 has native async/await support with some limitations, like missing HttpClient and possibly other classes.
WP7 had support for async/await in VS2010 using AsyncCTP, but in VS2012 it was re-added recently as Microsoft.Bcl.Async:
https://nuget.org/packages/Microsoft.Bcl.Async/1.0.12-beta