Lots of good questions, let's dig in. :)
Here's a great tutorial for interacting with the Storage Access Framework in KitKat:
https://developer.android.com/guide/topics/providers/document-provider.html#client
Interacting with the new APIs in Lollipop is very similar. To prompt the user to pick a directory tree, you can launch an intent like this:
Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT_TREE);
startActivityForResult(intent, 42);
Then in your onActivityResult(), you can pass the user-picked Uri to the new DocumentFile helper class. Here's a quick example that lists the files in the picked directory, and then creates a new file:
public void onActivityResult(int requestCode, int resultCode, Intent resultData) {
if (resultCode == RESULT_OK) {
Uri treeUri = resultData.getData();
DocumentFile pickedDir = DocumentFile.fromTreeUri(this, treeUri);
// List all existing files inside picked directory
for (DocumentFile file : pickedDir.listFiles()) {
Log.d(TAG, "Found file " + file.getName() + " with size " + file.length());
}
// Create a new file and write into it
DocumentFile newFile = pickedDir.createFile("text/plain", "My Novel");
OutputStream out = getContentResolver().openOutputStream(newFile.getUri());
out.write("A long time ago...".getBytes());
out.close();
}
}
The Uri returned by DocumentFile.getUri()
is flexible enough to use with may different platform APIs. For example, you could share it using Intent.setData()
with Intent.FLAG_GRANT_READ_URI_PERMISSION
.
If you want to access that Uri from native code, you can call ContentResolver.openFileDescriptor()
and then use ParcelFileDescriptor.getFd()
or detachFd()
to obtain a traditional POSIX file descriptor integer.
By default, the Uris returned through Storage Access Frameworks intents are not persisted across reboots. The platform "offers" the ability to persist the permission, but you still need to "take" the permission if you want it. In our example above, you'd call:
getContentResolver().takePersistableUriPermission(treeUri,
Intent.FLAG_GRANT_READ_URI_PERMISSION |
Intent.FLAG_GRANT_WRITE_URI_PERMISSION);
You can always figure out what persisted grants your app has access to through the ContentResolver.getPersistedUriPermissions()
API. If you no longer need access to a persisted Uri, you can release it with ContentResolver.releasePersistableUriPermission()
.
No, we can't retroactively add new functionality to older versions of the platform.
There's currently no UI that shows this, but you can find the details in the "Granted Uri Permissions" section of adb shell dumpsys activity providers
output.
Uri permission grants are isolated on a per-user basis, just like all other multi-user platform functionality. That is, the same app running under two different users has no overlaping or shared Uri permission grants.
The backing DocumentProvider can revoke permission at any time, such as when a cloud-based document is deleted. The most common way to discover these revoked permissions is when they disappear from ContentResolver.getPersistedUriPermissions()
mentioned above.
Permissions are also revoked whenever app data is cleared for either app involved in the grant.
Yep, the ACTION_OPEN_DOCUMENT_TREE
intent gives you recursive access to both existing and newly created files and directories.
Yep, multiple selection has been supported since KitKat, and you can allow it by setting EXTRA_ALLOW_MULTIPLE
when starting your ACTION_OPEN_DOCUMENT
intent. You can use Intent.setType()
or EXTRA_MIME_TYPES
to narrow the types of files that can be picked:
http://developer.android.com/reference/android/content/Intent.html#ACTION_OPEN_DOCUMENT
Yep, the primary shared storage device should appear in the picker, even on the emulator. If your app only uses the Storage Access Framework for accessing shared storage, you no longer need the READ/WRITE_EXTERNAL_STORAGE
permissions at all and can remove them or use the android:maxSdkVersion
feature to only request them on older platform versions.
When physical media is involved, the UUID (such as FAT serial number) of the underlying media is always burned into the returned Uri. The system uses this to connect you to the media that the user originally selected, even if the user swaps the media around between multiple slots.
If the user swaps in a second card, you'll need to prompt to gain access to the new card. Since the system remembers grants on a per-UUID basis, you'll continue to have previously-granted access to the original card if the user reinserts it later.
http://en.wikipedia.org/wiki/Volume_serial_number
In my Android project in Github, linked below, you can find working code that allows to write on extSdCard in Android 5. It assumes that the user gives access to the whole SD Card and then lets you write everywhere on this card. (If you want to have access only to single files, things get easier.)
Triggering the Storage Access Framework:
@TargetApi(Build.VERSION_CODES.LOLLIPOP)
private void triggerStorageAccessFramework() {
Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT_TREE);
startActivityForResult(intent, REQUEST_CODE_STORAGE_ACCESS);
}
Handling the response from the Storage Access Framework:
@TargetApi(Build.VERSION_CODES.LOLLIPOP)
@Override
public final void onActivityResult(final int requestCode, final int resultCode, final Intent resultData) {
if (requestCode == SettingsFragment.REQUEST_CODE_STORAGE_ACCESS) {
Uri treeUri = null;
if (resultCode == Activity.RESULT_OK) {
// Get Uri from Storage Access Framework.
treeUri = resultData.getData();
// Persist URI in shared preference so that you can use it later.
// Use your own framework here instead of PreferenceUtil.
PreferenceUtil.setSharedPreferenceUri(R.string.key_internal_uri_extsdcard, treeUri);
// Persist access permissions.
final int takeFlags = resultData.getFlags()
& (Intent.FLAG_GRANT_READ_URI_PERMISSION | Intent.FLAG_GRANT_WRITE_URI_PERMISSION);
getActivity().getContentResolver().takePersistableUriPermission(treeUri, takeFlags);
}
}
}
Getting an outputStream for a file via the Storage Access Framework (making use of the stored URL, assuming that this is the URL of the root folder of the external SD card)
DocumentFile targetDocument = getDocumentFile(file, false);
OutputStream outStream = Application.getAppContext().
getContentResolver().openOutputStream(targetDocument.getUri());
This uses the following helper methods:
public static DocumentFile getDocumentFile(final File file, final boolean isDirectory) {
String baseFolder = getExtSdCardFolder(file);
if (baseFolder == null) {
return null;
}
String relativePath = null;
try {
String fullPath = file.getCanonicalPath();
relativePath = fullPath.substring(baseFolder.length() + 1);
}
catch (IOException e) {
return null;
}
Uri treeUri = PreferenceUtil.getSharedPreferenceUri(R.string.key_internal_uri_extsdcard);
if (treeUri == null) {
return null;
}
// start with root of SD card and then parse through document tree.
DocumentFile document = DocumentFile.fromTreeUri(Application.getAppContext(), treeUri);
String[] parts = relativePath.split("\\/");
for (int i = 0; i < parts.length; i++) {
DocumentFile nextDocument = document.findFile(parts[i]);
if (nextDocument == null) {
if ((i < parts.length - 1) || isDirectory) {
nextDocument = document.createDirectory(parts[i]);
}
else {
nextDocument = document.createFile("image", parts[i]);
}
}
document = nextDocument;
}
return document;
}
public static String getExtSdCardFolder(final File file) {
String[] extSdPaths = getExtSdCardPaths();
try {
for (int i = 0; i < extSdPaths.length; i++) {
if (file.getCanonicalPath().startsWith(extSdPaths[i])) {
return extSdPaths[i];
}
}
}
catch (IOException e) {
return null;
}
return null;
}
/**
* Get a list of external SD card paths. (Kitkat or higher.)
*
* @return A list of external SD card paths.
*/
@TargetApi(Build.VERSION_CODES.KITKAT)
private static String[] getExtSdCardPaths() {
List<String> paths = new ArrayList<>();
for (File file : Application.getAppContext().getExternalFilesDirs("external")) {
if (file != null && !file.equals(Application.getAppContext().getExternalFilesDir("external"))) {
int index = file.getAbsolutePath().lastIndexOf("/Android/data");
if (index < 0) {
Log.w(Application.TAG, "Unexpected external file dir: " + file.getAbsolutePath());
}
else {
String path = file.getAbsolutePath().substring(0, index);
try {
path = new File(path).getCanonicalPath();
}
catch (IOException e) {
// Keep non-canonical path.
}
paths.add(path);
}
}
}
return paths.toArray(new String[paths.size()]);
}
/**
* Retrieve the application context.
*
* @return The (statically stored) application context
*/
public static Context getAppContext() {
return Application.mApplication.getApplicationContext();
}
https://github.com/jeisfeld/Augendiagnose/blob/master/AugendiagnoseIdea/augendiagnoseLib/src/main/java/de/jeisfeld/augendiagnoselib/fragments/SettingsFragment.java#L521
and
https://github.com/jeisfeld/Augendiagnose/blob/master/AugendiagnoseIdea/augendiagnoseLib/src/main/java/de/jeisfeld/augendiagnoselib/util/imagefile/FileUtil.java
SimpleStorage helps you by simplifying Storage Access Framework across API levels. It works with scoped storage as well. For example:
val fileFromExternalStorage = DocumentFileCompat.fromSimplePath(context, basePath = "Downloads/MyMovie.mp4")
val fileFromSdCard = DocumentFileCompat.fromSimplePath(context, storageId = "9016-4EF8", basePath = "Downloads/MyMovie.mp4")
Granting SD card's URI permissions, picking files & folders are simpler with this library:
class MainActivity : AppCompatActivity() {
private lateinit var storageHelper: SimpleStorageHelper
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
storageHelper = SimpleStorageHelper(this, savedInstanceState)
storageHelper.onFolderSelected = { requestCode, folder ->
// do stuff
}
storageHelper.onFileSelected = { requestCode, file ->
// do stuff
}
btnRequestStorageAccess.setOnClickListener { storageHelper.requestStorageAccess() }
btnOpenFolderPicker.setOnClickListener { storageHelper.openFolderPicker() }
btnOpenFilePicker.setOnClickListener { storageHelper.openFilePicker() }
}
override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
super.onActivityResult(requestCode, resultCode, data)
storageHelper.storage.onActivityResult(requestCode, resultCode, data)
}
override fun onSaveInstanceState(outState: Bundle) {
storageHelper.onSaveInstanceState(outState)
super.onSaveInstanceState(outState)
}
override fun onRestoreInstanceState(savedInstanceState: Bundle) {
super.onRestoreInstanceState(savedInstanceState)
storageHelper.onRestoreInstanceState(savedInstanceState)
}
}
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