Infopath 2013代码中FileQueryConnection的转换错误

Question

我一直在使用infopath表单将infopath 2007迁移到infopath 2013.要将数据绑定到DropDownList控件，已经使用了FileQueryConnection。

 // Retrieve the data connection bound to the Manager drop-down list box
 FileQueryConnection institutionConnection =(FileQueryConnection)DataConnections[ExternalUsersDC];
 // returned by the owssvr.dll with a filter on External Users of Institution
 institutionConnection.FileLocation = GetFileLocation(currentSite, externalUsersGuid, ExternalUserInstitution, institution);
 // Query the data connection to fill the Manager drop-down list box with items
 institutionConnection.Execute();

这里ExternalUsersDC是infopath连接文件的名称。 GetFileLocation方法获取列表物理位置，按预期正常工作。

尝试DataConnection到FileQueryConnection时发生转换错误。 错误信息如下;

无法转换“Microsoft.Office.InfoPath.Internal.SharePointListAdapterRWQueryAdapterHost”类型的对象以键入“Microsoft.Office.InfoPath.FileQueryConnection”

我到处寻找原因并失败了。 如果有人有这个问题的经验，请详细说明我的道路。

Answer 1

尝试AS运营商。 它将尝试转换为适当的类型。如果不能进行强制转换，它将通过返回NULL优雅地失败。

    FileQueryConnection institutionConnection =DataConnections[ExternalUsersDC] as FileQueryConnection;
 // returned by the owssvr.dll with a filter on External Users of Institution
 institutionConnection.FileLocation = GetFileLocation(currentSite, externalUsersGuid, ExternalUserInstitution, institution);
 // Query the data connection to fill the Manager drop-down list box with items
 institutionConnection.Execute();