Infopath 2013代碼中FileQueryConnection的轉換錯誤

Question

我一直在使用infopath表單將infopath 2007遷移到infopath 2013.要將數據綁定到DropDownList控件，已經使用了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();

這里ExternalUsersDC是infopath連接文件的名稱。 GetFileLocation方法獲取列表物理位置，按預期正常工作。

嘗試DataConnection到FileQueryConnection時發生轉換錯誤。 錯誤信息如下;

無法轉換“Microsoft.Office.InfoPath.Internal.SharePointListAdapterRWQueryAdapterHost”類型的對象以鍵入“Microsoft.Office.InfoPath.FileQueryConnection”

我到處尋找原因並失敗了。 如果有人有這個問題的經驗，請詳細說明我的道路。

Answer 1

嘗試AS運營商。 它將嘗試轉換為適當的類型。如果不能進行強制轉換，它將通過返回NULL優雅地失敗。

    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();