Android：SYSTEM_ALERT_WINDOW权限保护级别

Question

public static final String SYSTEM_ALERT_WINDOW

Allows an app to create windows using the type WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY , shown on top of all other apps. Very few apps should use this permission; these windows are intended for system-level interaction with the user.

Note: If the app targets API level 23 or higher, the app user must explicitly grant this permission to the app through a permission management screen. The app requests the user's approval by sending an intent with action Settings.ACTION_MANAGE_OVERLAY_PERMISSION . The app can check whether it has this authorization by calling Settings.canDrawOverlays().

Protection level: signature|preinstalled|appop|pre23|development

Constant Value: "android.permission.SYSTEM_ALERT_WINDOW"

https://developer.android.com/reference/android/Manifest.permission.html#SYSTEM_ALERT_WINDOW

Protection level: signature|preinstalled|appop|pre23|development

1) Protection level of SYSTEM_ALERT_WINDOW is signature but the permission is granted to normal app signed with different certificates.Is it becasue user explictly grants it , the signature become invalid here?

2)what are |preinstalled|appop|pre23|development Protection levels in android?

Thanks

Answer 1

Preinstalled means system application, starting from API level 23 protection level system is deprecated and preinstalled and privileged take the front row. If your app is pre-installed it will be able to exercise this permission. If your app has platform signature it can, or if your app has certificates that system can recognize