Scoped Storage Stories: The Undocumented Documents
Android 10 is greatly restricting access to external storage
via filesystem APIs. Instead, we need to use other APIs to work with content.
This is the 12th post in a seemingly never-ending series, where we will explore how to work with those
alternatives.
One apparent gap in the MediaStore options is the Documents/ directory. We
have obvious support for the media directories and Downloads/, but everything
else had to be handled via the Storage Access Framework. This includes Documents/, which,
like Downloads/, seems like it would be a general-purpose location.
As it turns out, there is support for Documents/. It���s just not documented.
This comes to us courtesy of Stack Overflow user blackapps, and
this answer.
To work with downloads, as we saw previously,
we can use MediaStore.Downloads as the basis. However, using
MediaStore.Files, we can work with Downlodads/ and Documents/, plus
custom subdirectories under those.
Specifically, MediaStore.Files.getContentUri("external") gets us a Uri
that we can use akin to MediaStore.Downloads.EXTERNAL_CONTENT_URI for inserting
new content and querying for our own content, though as before we cannot
access other apps��� content this way. If we use RELATIVE_PATH and specify
Documents, our content will go into the Documents/ directory:
val values = ContentValues().apply {
put(MediaStore.Files.FileColumns.DISPLAY_NAME, filename)
put(MediaStore.Files.FileColumns.MIME_TYPE, mimeType)
put(MediaStore.Files.FileColumns.RELATIVE_PATH, "Documents")
put(MediaStore.Files.FileColumns.IS_PENDING, 1)
}
val resolver = context.contentResolver
val uri =
resolver.insert(MediaStore.Files.getContentUri("external"), values)
uri?.let {
resolver.openOutputStream(uri)?.use { outputStream ->
val sink = outputStream.sink().buffer()
response.body?.source()?.let { sink.writeAll(it) }
sink.close()
}
values.clear()
values.put(MediaStore.Downloads.IS_PENDING, 0)
resolver.update(uri, values, null, null)
} ?: throw RuntimeException("MediaStore failed for some reason")
We can also use subdirectories under Documents/, such as Documents/AwesomeStuff.
And, we can use Downloads/ as the base. Attempts to write to other root directories
than Documents/ and Downloads/ will fail with an error.
You can even use this for removable volumes. blackapps��� answer shows a hard-coded
storage volume ID, though presumably using StorageManager and methods like
getStorageVolumes() will be more flexible.
The fact that this does not appear to be documented means that it is possible that
this will not be supported in future versions of Android. So, use this approach
with caution. But, if Documents/ is a must-have location, and you really want
to avoid the Storage Access Framework, MediaStore.Files may be something to consider.
The entire series of ���Scoped Storage Stories��� posts includes posts on:
The basics of using the Storage Access Framework
Getting durable access to the selected content
Working with DocumentFile for individual documents
Working with document trees
Working with DocumentsContract
Problems with the SAF API
A specific problem with listFiles() on DocumentFile
Storing content using MediaStore
Reading content from the MediaStore
Modifying MediaStore content from other apps
Limitations of MediaStore.Downloads
The undocumented Documents option
