Question

我正在使用Nuget包System.Threading.Tasks用于Silverlight 4（来自Mono的端口）。我一直得到InvalidOperationException（“基础任务已经处于三个最终状态之一：RanToCompletion，Faulted或Cancelled。”）以下内容：

var tasks = new Task<DeploymentCatalog>[2];

//Catalog the XAP downloaded by the Application Loader, the BiggestBox Index:
var uri0 = new Uri(Application.Current.

Host.InitParams["LoaderInfoXapPath"], UriKind.Relative);
tasks[0] = CompositionUtility.DownloadCatalogAsync(uri0);

//Catalog the XAP with the BiggestBox Index Part:
var uri1 = new Uri(Application.Current
    .Host.InitParams["BiggestBoxIndexXapPath"], UriKind.Relative);
tasks[1] = CompositionUtility.DownloadCatalogAsync(uri1);

//tasks did not run by default...
//tasks[0].Start();
//tasks[1].Start();

Task.WaitAll(tasks);

this.AddToAggregateCatalog(tasks[0].Result);
this.AddToAggregateCatalog(tasks[1].Result);

base.Compose();

其中DownloadCatalogAsync是：

/// <summary>
/// Downloads the catalog
/// in a <see cref="System.Threading.Task"/>.
/// </summary>
/// <param name="location">The location.</param>
/// <param name="downloadCompleteAction">The download complete action.</param>
[SuppressMessage("Microsoft.Reliability", "CA2000:DisposeObjectsBeforeLosingScope",
    Justification = "Reliable disposal depends on callers.")]
public static Task<DeploymentCatalog> DownloadCatalogAsync(Uri location)
{
    return DownloadCatalogAsTask(location, null);
}

/// <summary>
/// Downloads the catalog
/// in a <see cref="System.Threading.Task"/>.
/// </summary>
/// <param name="location">The location.</param>
/// <param name="downloadCompleteAction">The download complete action.</param>
/// <remarks>
/// For details, see the “Converting an Event-Based Pattern” section in 
/// “Simplify Asynchronous Programming with Tasks”
/// by Igor Ostrovsky
/// [http://msdn.microsoft.com/en-us/magazine/ff959203.aspx]
/// </remarks>
[SuppressMessage("Microsoft.Reliability", "CA2000:DisposeObjectsBeforeLosingScope",
    Justification = "Reliable disposal depends on callers.")]
public static Task<DeploymentCatalog> DownloadCatalogAsync(Uri location,
    Action<object, AsyncCompletedEventArgs> downloadCompleteAction)
{
    var completionSource = new TaskCompletionSource<DeploymentCatalog>();
    var catalog = new DeploymentCatalog(location);

    catalog.DownloadCompleted += (s, args) =>
    {
        if(args.Error != null) completionSource.SetException(args.Error);
        else if(args.Cancelled) completionSource.SetCanceled();
        else
        {
            completionSource.SetResult(s as DeploymentCatalog); //exception thrown here
            if(downloadCompleteAction != null)
                downloadCompleteAction.Invoke(s, args);
        }
    };

    catalog.DownloadAsync();

    return completionSource.Task;
}

我在WebClient使用相同的模式并且它工作正常（但我没有明确地Start()任务 - 但是我没有使用Mono测试WebClient任务并行库（适用于Silverlight）的移植版本。我想我应该这样做......

Answer 1

您正在调用TaskCompletionSource上的Start并且TCS任务已经启动，并且在您遇到此异常的情况下，它也已经完成。通常，您希望设计像DownloadCatalogAsTask这样的方法来返回已经启动的Task实例，并且调用者可以期望它们启动并避免自己调用Start。

结合其他建议：

我会考虑将方法重命名为DownloadCatalogAsync以符合.NET 4.5命名准则。
我不会通过动作＆lt;＆gt;进入异步方法。返回Task的重点是，您可以使用熟悉的模式（如显式的ContinueWith或C＃5.0中的await关键字）链接continuation。在这里，你发明了自己的方法。

Answer 2

我遇到了同样的问题。即Silverlight 4上的Mono TPL; completionSource.SetResult()引发的异常。

当我使用completionSource.TrySetResult()时，这已得到解决。

TaskCompletionSource <deploymentcatalog>？</deploymentcatalog>有什么问题

2 个答案: