How does Instagram customize the UIKeyboard returnKey to an '@' and a '#"?

Question

The most recent version of the Instagram iOS app does something interesting. When writing in a text field (e.g., posting a comment), the UIKeyboard's return key has been replaced by two keys: an @ key and a # key. Here's a screenshot:

I would like to know how they do this. As far as I can tell, @ and # keys behave like normal keys: they disappear in keyboards that do not usually have returnKey (such as the emoji keyboard), etc.

The only thing that occurs to me as of now is that the app is getting a reference to the UIKeyboard and looping through the subviews, finding and hiding the returnKey, then finding and moving the @ and # keys. Any other ideas?

Answer 1

That seems to be a text field whose keyboardType is set to UIKeyboardTypeTwitter, first introduced in iOS 5. It's exactly the same keyboard layout that is used by Tweet Sheets in iOS 5, with the return key being replaced by the @ and # keys respectively.

Since Instagram happens to use @ for referring to users and # for tagging posts, just like Twitter, I'm guessing that they're borrowing UIKeyboardTypeTwitter for convenient use with their own app.