I'm writing an AppKit app which needs to send HTML email. Unfortuantely there is no API in AppKit for doing so. There is however MFMessageComposeViewController in iOS/Catalyst.
The approach I have been using is to embed a "Mail Assistant" Catalyst helper app inside my main AppKit app's bundle. The main app launches this helper app when it needs to send HTML email. It has been working great.
(this approach was inspired by Drafts: https://docs.getdrafts.com/misc/mail-assistant)
Unfortunately, Xcode 11.4 does not seem to like Catalyst helper apps being inside the bundle of AppKit apps. When building using 11.4, I get the following error:
"Target Integrity: Building for macOS, but the embedded app 'Mail Assistant.app' was built for Mac Catalyst.
I can't see any real problem fundamentally with my approach, yet it seems Apple has decided to prevent this kind of AppKit-Catalyst cooperation.
Can anyone think of a workaround, or will I be forced to remove the HTML mail sending feature from my AppKit app?