It is extremely annoying and error prone to resize an image 13 times to make icons for Xcode… so here’s a shortcut that does it for you. I’m sure I missed a more clever way to do this, so improvements are more than welcome.
Hope this helps someone.
https://www.icloud.com/shortcuts/50fef7ccfb1644399415d2ad6a8ee92f
I used to do this with Automator, then discovered this and have used it for the last year.
Icon Set Creator by Nicolas Miari
Here is a modified version of your shortcut that takes advantage of a dictionary. Add to the dictionary (as an array) for the rest of your icon sizes. I hope this helps
https://www.icloud.com/shortcuts/96adee92efaa40268f869c5f43414be7
Thank you very much Brainyliving. I knew there had to be a better way. Here is the shortcut with the additional sizes added. I added an extra loop to account for the resizing of non-square images. Thank you again.
https://www.icloud.com/shortcuts/bc3eaac9ac5d415581ac279f93dcf7a9
@scottcoulter in the spirit of another iteration, here is V4 
You can take advantage of an IF statement to check for non-square Width and Height. Allows you to just maintain one dictionary with simplified logic.
Just sharing in the spirit of offering another way to approach the logic. I hope this helps — jay