OpenSharedItem for opening .MSG files showing Error in Outlook C#

问题

I am using the following code to open the signed/unsigned Outlook messages and I display the content in WebBrowser control.

Microsoft.Office.Interop.Outlook.Application app = new Microsoft.Office.Interop.Outlook.Application();
var item = app.Session.OpenSharedItem(msgfile) as Microsoft.Office.Interop.Outlook.MailItem;
string message = item.HTMLBody;
app.Session.Logoff();

It is working fine for the first time the file is opening, but after closing the Outlook file trying to reopen the file it showing the following error:

"Cannot open file: C:\tion.msg. The file may not exist, you may not have permission to open it, or it may be open in another program. Right-click the folder that contains the file, and then click Properties to check your permissions for the folder."

After some time later it is opening fine. For this strange behavior what could be the reason and how to rectify the the error message?

回答1:

Would any combination of the Quit[1], Close[2] or ReleaseComObject[3] methods work for you? My code worked better but not perfect after I used them.[4]

using Outlook = Microsoft.Office.Interop.Outlook;

.
.
.

var app = new Outlook.Application();
var item = app.Session.OpenSharedItem(msgfile) as Outlook.MailItem;

//Do stuff with the mail.

item.Close(OlInspectorClose.olDiscard);
app.Quit();
Marshal.ReleaseComObject(item);

Another solution, according to Microsoft - Help and Support[5], is to delay the opening of the file. However, it doesn't sound like a good solution to me since, like @SliverNinja also said, you'll never know when Outlook releases its lock of the file.

Notes and references

http://msdn.microsoft.com/en-us/library/microsoft.office.interop.outlook._application.quit.aspx, read 2014-10-14, 16:19.
http://msdn.microsoft.com/en-us/library/microsoft.office.interop.outlook._mailitem.close%28v=office.15%29.aspx, read 2014-10-14, 16:19.
http://msdn.microsoft.com/en-us/library/system.runtime.interopservices.marshal.releasecomobject.aspx, read 2014-10-14, 16:19.
For example, if I had opened Outlook for som regular work, the Quit-method would close that window as well.
http://support2.microsoft.com/kb/2633737, read 2014-10-08, 16:19.

回答2:

Outlook manages its own cache of items when you are opening and closing messages. Your best bet would be to use a randomly generated filename (i.e. Path.GetRandomFilename) when opening via OpenSharedItem so that you don't get issues. I would also use a temporary path instead of root c:\ (i.e. Path.GetTempPath).

You can try and free the MailItem reference (i.e. setting it to null), but there is no guarantee when Outlook will release the item from its cache.

回答3:

You can use Redemption for that - call RDOSession.GetMessageFromMsgFile.
If you need to release the message immediately after you are done, use Marshal.ReleaseComObject()
In case of Redemption, you can also cast RDOMail object to the IDisposable interface and call IDisposable.Dispose().