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今天分享android权限组（Permission groups）的概念，以及在android 6.0运行时提示访问权限的机制。

All dangerous Android system permissions belong to permission groups. If the device is running Android 6.0 (API level 23) and the app's targetSdkVersion is 23 or higher, the following system behavior applies when your app requests a dangerous permission:

If an app requests a dangerous permission listed in its manifest, an

d the app does not currently have any permissions in the permission group, the system shows a dialog box to the user describing the permission group that the app wants access to. The dialog box does not describe the specific permission within that group. For
example, if an app requests the READ_CONTACTS permission, the system dialog box just says the app needs access to the device's contacts. If the user grants approval, the system gives the app just the permission it requested.
If an app requests a dangerous permission listed in its manifest, and the app already has another dangerous permission in the same permission group, the system immediately grants the permission without any interaction with the user. For example, if an app
had previously requested and been granted the READ_CONTACTS permission, and it then requests WRITE_CONTACTS, the system immediately grants that permission.

Any permission can belong to a permission group, including normal permissions and permissions defined by your app. However, a permission's group only affects the user experience if the permission is dangerous. You can ignore the permission group for normal
permissions.

If the device is running Android 5.1 (API level 22) or lower, or the app's targetSdkVersion is 22 or lower, the system asks the user to grant the permissions at install time. Once again, the system just tells the user what permission groups the app needs,
not the individual permissions.

Table 1. Dangerous permissions and permission groups.

READ_CONTACTS	Permissions
CALENDAR	READ_CALENDAR WRITE_CALENDAR
CAMERA	CAMERA
CONTACTS	READ_CONTACTS WRITE_CONTACTS GET_ACCOUNTS
LOCATION	ACCESS_FINE_LOCATION ACCESS_FINE_LOCATION
MICROPHONE	RECORD_AUDIO
PHONE	READ_PHONE_STATE CALL_PHONE READ_CALL_LOG WRITE_CALL_LOG ADD_VOICEMAIL USE_SIP PROCESS_OUTGOING_CALLS
SENSORS	BODY_SENSORS
SMS	SEND_SMS RECEIVE_SMS READ_SMS RECEIVE_WAP_PUSH RECEIVE_MMS

STORAGE

READ_EXTERNAL_STORAGE WRITE_EXTERNAL_STORAGE