自定义工作流程活动错误“值不能为空”

Question

我正在 VS2010 中创建一个针对 .NET 3.5 的自定义工作流活动。该 DLL 实际上正在 Microsoft System Center Service Manager 自定义工作流程中使用，但我认为这不是我的问题。

我有一个公共字符串属性，用户可以输入活动应使用的字符串。但是，当 WF 运行时，它会出错“值不能为空”。我想确定它是我的代码还是其他东西。

当我们将自定义活动拖到设计器上时，我可以在设计器上输入该属性的字符串文本。

public static DependencyProperty ChangeRequestStageProperty = DependencyProperty.Register("ChangeRequestStage", typeof(String), typeof(UpdateChangeRequestStage));

    [DescriptionAttribute("The value to set the ChangeRequestStage Property in the ChangeRequest Extension class.")]
    [CategoryAttribute("Change Request Extension")]
    [BrowsableAttribute(true)]
    [DesignerSerializationVisibilityAttribute(DesignerSerializationVisibility.Visible)]
    public String Stage
    {
        get { return ((String)(base.GetValue(UpdateChangeRequestStage.ChangeRequestStageProperty))); }
        set { base.SetValue(UpdateChangeRequestStage.ChangeRequestStageProperty, value); }
    }

    protected override ActivityExecutionStatus Execute(ActivityExecutionContext executionContext)
    {
        EnterpriseManagementGroup emg = CreateEMG();

        //System.WorkItem.ChangeRequest Extension - ClassExtension_928bec0a_cac4_4a0a_bd89_7146c9052fbe
        ManagementPackClass mpcChangeRequest = emg.EntityTypes.GetClass(new Guid("8c6c6057-56ad-3862-47ec-dc0dde80a071"));

        //System.WorkItemContainsActivity Relationship Class
        ManagementPackRelationship workItemContainsActivityRelationship = emg.EntityTypes.GetRelationshipClass(new Guid("2DA498BE-0485-B2B2-D520-6EBD1698E61B"));

        EnterpriseManagementObject changeRequest = null;

        //Loop thru each emo (Change Request in this case), and assign it. There will never be more than 1 emo returned
        foreach (EnterpriseManagementObject obj in emg.EntityObjects.GetRelatedObjects<EnterpriseManagementObject>(executionContext.ContextGuid, workItemContainsActivityRelationship, TraversalDepth.OneLevel, ObjectQueryOptions.Default))
        { changeRequest = obj; }

        EnterpriseManagementObjectProjection emop = new EnterpriseManagementObjectProjection(changeRequest);

        if (emop != null)
        { emop.Object[mpcChangeRequest, "ChangeRequestStage"].Value = Stage; }

        emop.Commit();

        return base.Execute(executionContext);
    }

由于它收到“值不能为空”错误，我猜测它在这一行：

emop.Object[mpcChangeRequest, "ChangeRequestStage"].Value = Stage;

我将测试并查看对值进行硬编码是否有效。有什么想法吗？ 在此输入代码

Answer 1

试试这个

if (emop != null && emop.Object[mpcChangeRequest, "ChangeRequestStage"] != null)
   emop.Object[mpcChangeRequest, "ChangeRequestStage"].Value = Stage

Answer 2

我不想让这个问题悬而未决，所以我正在更新我如何解决这个问题（很久以前）。

我没有使用 EnterpriseManagementObjectProjection (emop)，而是使用标准 EnterpriseManagementObject (emo)。从那里，我能够遵循上面类似的格式：

ManagementPackClass mpcChangeRequest = emg.EntityTypes.GetClass(new Guid("8c246fc5-4e5e-0605-dc23-91f7a362615b"));
changeRequest[mpcChangeRequest, "ChangeRequestStage"].Value = this.Stage;
changeRequest.Commit();