These two instructional videos demonstrated detailed steps of how to set up the iOS to use the switch interface.
After having connected to the Adafruit Bluefruit EZ-Key from the iOS settings, here shows how I set the button actions. The button with circles was set as the tapping action. The button with lines is set as selection menu and the square is the home button on the iPad. The one-button version with the square button cover was connected to the two-button version through the 3.5mm jack.
More switch accessible apps can be found at http://www.atandme.com/?p=467.
Similarly, the Mac OS, Yosemite, can be also set to use the switch interface in the System Preferences/Accessbility. Here is a video shows how a wheelchair user managed to do incredible work on the Mac. There are a lot of settings and tips that the user can set customized on-screen buttons and frequent used functions to fit user's needs.
For more detail of switch control on Mac OS, the Apple support has the most updated information (https://support.apple.com/en-us/HT202865). I recently upgraded to the Sierra and the BOSI seems working fine with it.