CKShare provides a url that allows others to be invited. It is necessary for a potential participant to have access to this url (otherwise there is no way for them to accept the invitation). An easy solution is to send this url via the Messages application, but this is an extra step for the share owner. I have noticed that Apple's Passwords app somehow sends this url to the invited user within the Passwords app - and I wonder if this is possible with just public Apple apis, or if Apple uses some private api to achieve this.
"An easy solution is to send this url via the Messages application, but this is an extra step for the share owner."
Yeah, participants need to have the share URL (CKShsare.url). If you use the system provided share UI (ShareLink, etc), it allows you to send the link via Message, Mail, and etc.
You don't have to rely on the system provided share UI to implement your sharing flow though. If you implement the sharing flow in your own way, as discussed in Implement a custom sharing flow, you can retrieve the share URL after successfully saving the share, and send it in your own way.
Best,
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Ziqiao Chen
Worldwide Developer Relations.