C# Outlook VSTO add-in error while trying to get item in an Exchange setup

问题

I'm developing an Office VSTO add-in in C# which looks up calendar appointments in Outlook, and reads/writes some data in them.

Recently, one of the clients had issues with the add-in, namely they can't read/write the calendar appointment, and it throws an exception :

The operation failed.

There's not much info from the exception log, but I suspect they have synchronization problems with Exchange.

I asked the client, and they said, that they also have a random popup in Outlook as well, which sometimes happens when there's a mishap while syncing with Exchange. I told them to 'repair' the Outlook data files, but that didn't fix the problem.

The outlook items are basically looked up based on their Outlook EntryIDs OR a Subject (the subjects are unique, and for the sake of simplicity I translated the code a little bit)

...main alghorythm...
    Outlook.AppointmentItem calAppointment = null;
    calAppointment = SearchforCalendarMatch(EntryID, Subject); //we try to find either by EntryID or by Subject
    if (calAppointment != null)
    {
        calAppointment.Start = StartDate;
        calAppointment.End = FinishDate;
        calAppointment.Body = Notes;
        calAppointment.Save(); //we're changing the found calendar appointment here
    }
...

public Outlook.AppointmentItem SearchforCalendarMatch(String EntryID, String Subject)
{
    Outlook.NameSpace ns = null;
    Outlook.MAPIFolder calendarFolder = null;
    Outlook.Items calendarFolderItems = null;
    Outlook.Items filteredcalendarFolderItems = null;
    Outlook.AppointmentItem calAppointment = null;

    Outlook.Application OutlookApp = new Outlook.Application();
    outlookversion = OutlookApp.Version;
    ns = OutlookApp.Session;

    //Try to find the calendar appointment by the EntryID
    dynamic OutlookItem = ns.GetItemFromID(t.Text28);
    if (OutlookItem != null)
    {
        if (OutlookItem is Outlook.AppointmentItem)
        {
            Outlook.AppointmentItem foundItem = (Outlook.AppointmentItem)OutlookItem;
            return foundItem;
        }
    }

    //If the EntryID was missing, we try to find the calendar appointment by the Subject. 
    //(original code is very long, and there are multiple things here, but let's just assume that 100% sure that the subject is unique, so it will find it)
    String SubjectMatch = "[Subject] = '" + Subject + "'";
    filteredcalendarFolderItems = calendarFolderItems.Restrict(SubjectMatch);
    for (int i = 1; i <= filteredcalendarFolderItems.Count; i++)
    {
        //appointment has to be one of these
        calAppointment = (Microsoft.Office.Interop.Outlook.AppointmentItem)filteredcalendarFolderItems[i];
        if (!calAppointment.IsConflict) //conflict check here, not sure if it helps at all
        {
            return calAppointment; //this is not the complete code, but this is the basic idea of it.
        }
    }
}

Any ideas how I could make the application recognize these failed Exchange syncs, and handle them differently?

I would still like to sync in these cases, if it's possible... (change the 'local data' in Outlook, then let Outlook handle everything from that on)

回答1:

You need to release underlying COM objects instantly. Use System.Runtime.InteropServices.Marshal.ReleaseComObject to release an Outlook object when you have finished using it. This is particularly important if your add-in attempts to enumerate more than 256 Outlook items in a collection that is stored on a Microsoft Exchange Server. If you do not release these objects in a timely manner, you can reach the limit imposed by Exchange on the maximum number of items opened at any one time. Then set a variable to Nothing in Visual Basic (null in C#) to release the reference to the object. Read more about that in the Systematically Releasing Objects article.

来源：https://stackoverflow.com/questions/43782786/c-sharp-outlook-vsto-add-in-error-while-trying-to-get-item-in-an-exchange-setup