Integrating drop-shipping into a IOS application? or direct Drop-shipping with merchants?

Hey all,
I am a self-taught IOS developer who is interested in e-commerce.
I've done a lot of research online about drop-shipping and I am very thankful to have found this forum!

My question being... Is there any software I can integrate into IOS, which will allow me to use Shopify (or any other drop-shipping tools) within my Iphone app? I want my online store to have a lot more functionality than Shopify or Wordpress etc can offer.

Or, will I need to set up relationships with each merchant directly to organise drop-shipping? And how would this work with inventory within the app?
I.e. How could I set up my inventory to be linked to my merchants inventory, to prevent any over-selling of a product?


I don't really have a niche, just a business model that requires a large amount of products to be listed within the app.
I know a niche is important, Im just doing my research as I am very keen to give e-commerce a go!

Any help or input would be greatly appreciated!

Thank you,
from New Zealand