How do I implement a slide-out drawer on the Android's call screen?

The Android app Thrutu puts a drawer on top of the in call screen which has several functions and only takes up a fraction of the 开发者_运维百科screen. The call control buttons below still are fully functional. Even a transparent activity would not allow this behaviour. Any idea on how to implement this?

The trick to making the underlying buttons work is to implement the UI using a Service rather than an Activity, make the Window you add (using WindowManager.addView) one of the higher-priority types (e.g. TYPE_PHONE), then use FLAG_NOT_TOUCH_MODAL.

I think you need android.permission.SYSTEM_ALERT_WINDOW.

Take a look at How to display a fullscreen TYPE_SYSTEM_ALERT window? and in particular Creating a system overlay where the home buttons still work?