I am trying to write an import of a 3rd party file format in my macOS sandboxed app. The file the user opens is a Json document, and inside this document is a url pointing to some required external data file. In this case it is the relative path to a local binary data file. I can create an absolute path to this file but I cannot open it with [NSData datawithcontentsoffile: path] because my app is sandboxed (on macOS App Store). If I turn off sandbox then I can open the external binary file.
What are some good strategies to open the external file in a sand boxed app? I’m thinking of opening a second nsopenpanel and asking the user to select the other file, but that seems awkward.