On Android it takes the name of the file and you are done. On iOS however it is a bit more complex.
There are a few steps you should take:
- Double check the font files are included in the Target in XCode
- Make sure they are included in the step “Copy Bundle Resources” (add files, not folders)
- Include them in the Info.plist of the app
- Find the name of the Font through FontBook or with some log statements in your AppDelegate
Explained in more detail here:
http://codewithchris.com/common-mistakes-with-adding-custom-fonts-to-your-ios-app/