How to create an UI or a widget that sits on top of all applications in Android?

Question

Can I create an UI or a widget in Android that will sit on top of all applications? There are applications that have widgets like this. One example has a camera icon on top

Answer 1

The following are more options for how the view is displayed.

This will make it an overlay on top of everything (including lock screen), but not clickable. WindowManager.LayoutParams. TYPE_SYSTEM_OVERLAY

This will make it clickable, but it won't be over the lock screen WindowManager.LayoutParams.TYPE_SYSTEM_ALERT

This will make it above everything (including lock screen) AND clickable. WindowManager.LayoutParams.TYPE_SYSTEM_ERROR

One thing to note about using "TYPE_SYSTEM_ERROR". If you wire-in a click event, anything it invokes will happen behind the lock screen.