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自定义工作流中使用，但我不认为这是我的问题。

我有一个公共字符串属性，用户键入活动应该使用的字符串。但是，当WF运行时，它会错误输出'value not not null'。如果是我的代码或其他内容，我想定位。

当我将自定义活动拖到设计器上时，我可以在设计器上为该属性键入字符串的文本。

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);
    }

因为它得到'值不能为空'错误，我猜这是在这一行：

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

我将测试并查看硬编码值是否有效。有任何想法吗？在这里输入代码

Answer 1

试试这个

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

Answer 2

我不想大开这个问题，所以我正在更新它（我很久以前）的解决方法。

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

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

自定义工作流活动错误'值不能为空'

2 个答案: