I want to create an Android Style share feature for my app. I created a share extension which gets called when you select pictures inside the stock photo app and press share. Now I want those pictures to be sent to the main app and get handled over there. My question is now:
Currently there's no way to do this. A share extension cannot open the containing app.
The intended approach for share extensions is that they handle all of the necessary work themselves. Extensions can share code with their containing apps by using custom frameworks, so in most cases that's no problem.
If you want to make data available to your app, you can set up an app group so that you have a shared directory. The extension can write data there, and the app can read it. That won't happen until the next time the user launches the app, though.