Question

我有一个控制器操作，它获取文档类型列表，然后为每个文档类型进行Web服务调用。我想立刻制作这些，所以循环它们只需要最长的一个。我不知道我的代码是否正确，我还需要做其他事情，或者我的代码是不正确的。

动作：

public ActionResult GetPlan(MemberViewModel request)
{
    DocService ds = new DocService();

    List<DocType> docTypes = ds.GetDocTypesForPlan(request.PlanId);

    List<CoverageDocument> coverageDocuments = ds.GetDocumentsForDocTypes(docTypes);

    return View(coverageDocuments);
}

GetDocumentsForDocTypes：

public List<CoverageDocument> GetDocumentsForDocTypes(List<DocType> planDocTypes)
{
    List<CoverageDocument> planDocuments = new List<CoverageDocument>();

    DocumentUtility documentUtility = new DocumentUtility();
    int lastYear = DateTime.Now.Year - 1;

    planDocTypes.ForEach(async (docType) =>
    {
        DocumentUtility.SearchCriteria sc = new DocumentUtility.SearchCriteria();
        sc.documentType = docType;
        Dictionary<long, Tuple<string, string>> documentList = await documentUtility.FindDocuments(sc);

        documentList.ToList().ForEach((document) =>
            {
                CoverageDocument doc = this.coverageDocumentConstructor(document);
                planDocuments.Add(doc);
            });
    });

    return planDocuments;
}

例外：

附加信息：无法启动异步操作这次。异步操作只能在一个内部启动异步处理程序或模块或在页面中的某些事件期间生命周期。如果在执行页面时发生此异常，请确保页面标记为＆lt;％@ Page Async =“true”％＆gt;。这个例外可能还表示尝试调用“异步void”方法，即通常在ASP.NET请求处理中不受支持。相反，异步方法应该返回一个Task，并且调用者应该等待它

Answer 1

您的代码不正确。通过向ForEach扩展方法发送异步lambda，您强制它为async void，这在UI事件处理程序之外永远不是一个好主意。

要实际上是异步的，您的呼叫需要始终保持异步：

public async Task<ActionResult> GetPlan(MemberViewModel request)
{
    DocService ds = new DocService();

    List<DocType> docTypes = ds.GetDocTypesForPlan(request.PlanId);

    List<CoverageDocument> coverageDocuments = await ds.GetDocumentsForDocTypesAsync(docTypes);

    return View(coverageDocuments);
}

public async Task<List<CoverageDocument>> GetDocumentsForDocTypesAsync(List<DocType> planDocTypes)
{
    DocumentUtility documentUtility = new DocumentUtility();
    int lastYear = DateTime.Now.Year - 1;

    var planDocuments = await Task.WhenAll(planDocTypes.Select(async (docType) =>
    {
        DocumentUtility.SearchCriteria sc = new DocumentUtility.SearchCriteria();
        sc.documentType = docType;

        return await documentUtility.FindDocuments(sc).Select((document) => this.coverageDocumentConstructor(document))
    }));

    return planDocuments.SelectMany(doc => doc);;
}

在Controller Action中进行异步调用

1 个答案: