I'm using the UIDocumentInteractionController method to share images from my app to WhatsApp (explained in How send image to WhatsApp from my application?, WhatsApp image sharing iOS).
I'm also aware of the share via URI option, used to share texts only (explained here: https://www.whatsapp.com/faq/iphone/23559013).
Is there a way to share both an image and a caption in a single share?
Currently there is no way that you can share both image and text together on whatsapp. Sharing both image and text together is not handled from the whatsapp side.
So, at a time you can share only image or text.