not quite minimalistic enough  

2020-09-18

MailItem in changing times.

According to the documentation, the first parameter of the Reply (and ReplyAll, and Forward) events on a MailItem event in Outlook is “the new item being sent in response to the original message”.

Uh, no. At least in VSTO; not sure about VBA, but I cannot see how it could be different there given that VSTO is a wrapper around the same COM interfaces. The argument is the original item that is being responded to:

void OnReply(object Response, ref bool Cancel)
{
    Cancel = false;

    if (Response is Outlook.MailItem item) {
        string html = item.HTMLBody;
        int pos = html.LastIndexOf("</body>");
        item.HTMLBody = html.Insert(pos, "This is the modified item. ");
    }
}

After this handler runs, the original item that was replied to will have the new sentence at the end, while the reply is entirely original. I suppose this means that the response message is created first, and then the event fires with the wrong argument.

Helpfully, though, when using Outlook’s preview/reading pane (whatever its name is this afternoon) the InlineResponse event on the Explorer object actually gets the correct message, i.e. the new one.

Trust Issues

After developing a new Outlook VSTO add-in, I noticed that at the first start after installing it (by the MSI method), Outlook would display a trust warning. The add-in is unsigned, but this should still not happen based on my experience from other add-ins.

As it turns out, there are two ways to “grant trust to the solution”:

The latter presumably works because Office assumes that write access to Program Files is sufficient evidence of administrative intent.

My installation path was C:\Program Files\Some Company\SomeAddin.

Huh. Now what?

… oh no, they didn’t …

… yes, they did.

Can you guess?

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OK, a hint. The “Program Files” directory?

S
P
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Either you have figured it out by now, or are hungry for the solution (because why else would you still be reading this?), so here it is:

The “Program Files” directory they talk about is the same “Program Files” directory that Office is installed in. My scenario involved a .NET assembly compiled to MSIL, so naturally I put it into the 64-bit Program Files directory because that one is more native to the system. The Office installation, however, was still 32-bit, and Outlook came to the (well, partially) unreasonable conclusion that:

"C:\Program Files\" != "C:\Program Files (x86)\"

Therefore the add-in was not installed in the Program Files directory, and therefore not to be trusted by default.

2020-09-16

A Bitmap, wrapped in a knotted Ribbon.

Writing Office add-ins has always been a bit of a dark art because there is not really all that much documentation, and what there is, tends to, let’s say, have been overtaken by events.

This is particularly true where VSTO, the Visual Studio Tools for Office, otherwise known as the .NET wrappers around the COM add-in API, is concerned. Even a seemingly simple task like finding out correct signatures for callback methods can be surprisingly difficult because the authoritative page still only mentions Office 2007, and you can never know what may have changed in the last 13 years. (Wow. Has it been that long?)

OK, enough of the empty complaining. Let’s get to the useful information. Everything below is based on current Office 365 with the latest VSTO version as of today, 10.0.60724.

The loadImage callback

The correct C# signature for the callback method named in <customUI loadImage="LoadImageCallback"> is:

public Bitmap LoadImageCallback(string imageId)

There are various discussions around the Internet on whether this method should return Bitmap or stdole.IPictureDisp, or whether Bitmap works everywhere except Outlook.

Bitmap works everywhere including Outlook.

Namespaces and idQ

When using the idQ attribute to identify controls, you may notice that your callbacks aren’t. Called, that is. This is explained in a paragraph about one-third down the page linked above:

If you use a COM add-in to customize the Fluent UI, the namespace name must be the ProgID of the COM add-in, but the behavior is otherwise the same. When you use a shared add-in, the ProgID is AddInName.Connect. When you use Microsoft Visual Studio 2005 Tools for the 2007 Microsoft Office System (Visual Studio 2005 Tools for Office Second Edition) to create the add-in, the ProgID is the name of the add-in.

(Emphasis mine.)

VSTO is actually older than the W3C recommendation on “Namespaces in XML 1.0”, Second Edition, so I have to admit that the idea did not contradict the spec at the time. (The original recommendation from 1999 mentioned that the intent was to use URIs, but did not yet require it.)

However, I fail to see the reason why the namespace ID must be the add-in’s name, unless it is the result of a very ugly shortcut in the implementation of the “Fluent” UI, i.e. the Ribbon. It would be entirely simple for the host application to associate any string with the add-in whose GetCustomUI() returned the particular bit of XML.

By the way, the “name of the add-in” in the VSTO case above, that the namespace ID has to match, is the name of the subkey of SOFTWARE\Microsoft\Office\...\Addins. In addition to being true empirically, it also matches the non-VSTO case because the only place where the ProgID is involved in the process of loading an add-in is that Registry key.