Background
----------

Android had a lot of changes as to how to handle the SD-card and storage in general:

* API 3 - you get all access, no permission needed
* API 4-15 - you need to use WRITE\_EXTERNAL\_STORAGE, and you get all access.
* API 16-18 - if you wish only to read, use READ\_EXTERNAL\_STORAGE
* API 19-20 - you can't read or write to secondary external storage (SD-card), unless your app is a system app, or you have root.
* API 21-22 - in order to access the SD-card, you need to ask the user for permission, and use the DocumentFile API instead of the File API. This raied a lot of questions, as I've written about [**here**](https://stackoverflow.com/q/26744842/878126), [**here**](https://stackoverflow.com/q/31662055/878126) and [**here**](https://stackoverflow.com/q/32019734/878126).

Starting with API 23 (Android 6), things seem to change yet again...

The problem
-----------

For API 23, there are at least 2 things that are new and are storage-related :

* "[**Adoptable Storage Devices**](https://developer.android.com/preview/behavior-changes.html#behavior-adoptable-storage)" - The user can optionally make the SD-card as something that's like the primary external storage.
* As part of the [**new permissions mechanism**](https://developer.android.com/preview/features/runtime-permissions.html#coding) (requesting permissions at runtime), it seems that storage is also a permission the user needs to confirm. This is for both READ\_EXTERNAL\_STORAGE and WRITE\_EXTERNAL\_STORAGE

Since there is no Android 6 device out there that has SD-card, and because the emulator itself doesn't really have the ability to use an SD-card, it's still impossible to know what's going on.

The questions
-------------

1. Will the SD-card get the access using the File-API instead of DocumentFile?
2. If I want access to all external storage paths (including SD-card), does this mean I need to request this permissions twice: one for the primary external storage and one for the SD-card?
3. Are files on the SD-card accessible in any way before the manual granting of the permission?
4. Suppose the user has chosen to use "Adoptable Storage Devices", what does it mean for the various functions that retrieve the paths of the app's files? For example : getFilesDir, getExternalFilesDir,... ? Would the oder of getExternalFilesDirs change because of it?
5. What happens to the files of the app when the user moves the app from/to the SD-card (using the "Adoptable Storage Devices") ? What about the app's files on the SD-card? Would they stay? Or would they move somewhere?

For example, if the app has "file1.txt" on the SD-card, on path "/storage/extSdCard/Android/data/appPackageName", and it has a file "file2.txt" (or even the same name) on the primary external storage on path "/storage/emulated/0/Android/data/appPackageName". After switching, what would happen for those files? How would they merge into a single folder, if at all?
6. When moving the app to the SD-card (using "Adoptable Storage Devices"), does it mean no internal storage will be used?