silverlight - 找不到 async 修饰符所需的所有类型

Question

我收到以下两个编译器错误(Resharper 7.0.1 没有报告错误):

Predefined type 'System.Runtime.CompilerServices.IAsyncStateMachine' is not defined or imported

Cannot find all types required by the 'async' modifier. Are you targeting the wrong framework version, or missing a reference to an assembly?

但这段代码不会编译:

public class Class1
{
    public Class1()
    {
        Um();
    }
    public async Task<DownloadStringCompletedEventArgs> Um()
    {
        var client = new WebClient();
        return await Observable.FromEvent<DownloadStringCompletedEventHandler, DownloadStringCompletedEventArgs>(x => client.DownloadStringCompleted += x,
                                    x => client.DownloadStringCompleted -= x);
    }
}

我见过 MSBuild doesn't find async required references已经除了我有 VS 2012 NOT VS 11 Beta - 尽管它已安装。我也在一个全新的程序集中尝试了它，没有指向应用程序的 xaml 命名空间。

Answer 1

您需要 Async Targeting Pack支持async在 Silverlight 5 中。