Tumblr for iOS now exposes URL schemes that can be invoked in order to create text, quote, link, and chat posts. Additionally, developers can specify callback URLs that will send the user back to their apps once the Tumblr post is either created or cancelled. These endpoints are now wrapped and exposed by the TMTumblrAppClient class, or the URLs can be accessed directly if you’d prefer (they’re documented here).
Lastly, Tumblr for iOS has been able to create photo and video posts using media shared from other apps for some time now, via Apple’s standard UIDocumentInteractionController. As of 3.3.1, third-party applications can now also specify captions and tags to accompany the photos and videos being shared. The annotations used to do so are documented here.
If you’re using the Tumblr iOS SDK in your app or plan to integrate going forward, please get in touch and let me know if there’s anything I can do to make this even easier.