我正在使用Android 11 (SDK版本30)编写一款新的应用程序，但是我简单地找不到有关如何将文件保存到外部存储的示例。
我阅读了他们的文档，现在知道他们基本上忽略了清单权限(READ_EXTERNAL_STORAGE和WRITE_EXTERNAL_STORAGE)。他们还忽略了manifest.xml应用程序标记中的android:requestLegacyExternalStorage="true"。
在他们的文档https://developer.android.com/about/versions/11/privacy/storage中，他们写道您需要启用DEFAULT_SCOPED_STORAGE和FORCE_ENABLE_SCOPED_STORAGE标志以在应用程序中启用作用域存储。
我需要在哪里启用这些标志？当我完成后，如何获得实际的写入外部存储权限？有人可以提供有效的代码吗？
我想要保存.gif、.png和.mp3文件。所以我不想写入图库。
提前感谢。
适用于所有API，包括API 30，Android 11：
public static File commonDocumentDirPath(String FolderName)
{
File dir = null;
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R)
{
dir = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOCUMENTS) + "/" + FolderName);
}
else
{
dir = new File(Environment.getExternalStorageDirectory() + "/" + FolderName);
}
// Make sure the path directory exists.
if (!dir.exists())
{
// Make it, if it doesn't exit
boolean success = dir.mkdirs();
if (!success)
{
dir = null;
}
}
return dir;
}
现在，使用这个commonDocumentDirPath保存文件。
顺便提一下，从评论中得知，getExternalStoragePublicDirectory在特定的作用域下现在可以在Api 30、Android 11上使用了。感谢CommonsWare的提示。
您可以将文件保存到外部存储的公共目录中，
例如文档、下载、相机拍摄的图片等等。
像以前10版本之前一样使用通常的方式即可。
private void createFile(String title) {
Intent intent = new Intent(Intent.ACTION_CREATE_DOCUMENT);
intent.addCategory(Intent.CATEGORY_OPENABLE);
intent.setType("text/html");
intent.putExtra(Intent.EXTRA_TITLE, title);
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
intent.putExtra(DocumentsContract.EXTRA_INITIAL_URI, Uri.parse("/Documents"));
}
createInvoiceActivityResultLauncher.launch(intent);
}
private void createInvoice(Uri uri) {
try {
ParcelFileDescriptor pfd = getContentResolver().
openFileDescriptor(uri, "w");
if (pfd != null) {
FileOutputStream fileOutputStream = new FileOutputStream(pfd.getFileDescriptor());
fileOutputStream.write(invoice_html.getBytes());
fileOutputStream.close();
pfd.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
/////////////////////////////////////////////////////
// You can do the assignment inside onAttach or onCreate, i.e, before the activity is displayed
String invoice_html;
ActivityResultLauncher<Intent> createInvoiceActivityResultLauncher;
@Override
protected void onCreate(Bundle savedInstanceState) {
invoice_html = "<h1>Just for testing received...</h1>";
createInvoiceActivityResultLauncher = registerForActivityResult(
new ActivityResultContracts.StartActivityForResult(),
result -> {
if (result.getResultCode() == Activity.RESULT_OK) {
// There are no request codes
Uri uri = null;
if (result.getData() != null) {
uri = result.getData().getData();
createInvoice(uri);
// Perform operations on the document using its URI.
}
}
});
我使用这种方法，它对我真的很有效。 我希望我能帮助你。如果有不清楚的地方，请随时问我。
Bitmap imageBitmap;
OutputStream outputStream ;
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q)
{
ContentResolver resolver = context.getContentResolver();
ContentValues contentValues = new ContentValues();
contentValues.put(MediaStore.MediaColumns.DISPLAY_NAME,"Image_"+".jpg");
contentValues.put(MediaStore.MediaColumns.MIME_TYPE,"image/jpeg");
contentValues.put(MediaStore.MediaColumns.RELATIVE_PATH,Environment.DIRECTORY_PICTURES + File.separator+"TestFolder");
Uri imageUri = resolver.insert(MediaStore.Images.Media.EXTERNAL_CONTENT_URI,contentValues);
try {
outputStream = resolver.openOutputStream(Objects.requireNonNull(imageUri) );
imageBitmap.compress(Bitmap.CompressFormat.JPEG,100,outputStream);
Objects.requireNonNull(outputStream);
Toast.makeText(context, "Image Saved", Toast.LENGTH_SHORT).show();
} catch (Exception e) {
Toast.makeText(context, "Image Not Not Saved: \n "+e, Toast.LENGTH_SHORT).show();
e.printStackTrace();
}
}
清单文件（添加许可）
<uses-permission android:name="android.permission.ACCESS_MEDIA_LOCATION" />
我知道这个问题有点老了，但是这里有一个可行的解决方案，可以在除了根目录之外的任何地方组织您的文件。
首先，在您的build.gradle文件中，实现SAF框架的DocumentFile类：
implementation 'androidx.documentfile:documentfile:1.0.1'
接下来调用此方法请求权限以使 SAF 正常运行（用户安装后只需执行一次）：
private void requestDocumentTreePermissions() {
// Choose a directory using the system's file picker.
new AlertDialog.Builder(this)
.setMessage("*Please Select A Folder For The App To Organize The Videos*")
.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
@RequiresApi(api = Build.VERSION_CODES.Q)
@Override
public void onClick(DialogInterface dialog, int which) {
StorageManager sm = (StorageManager) getSystemService(Context.STORAGE_SERVICE);
Intent intent = sm.getPrimaryStorageVolume().createOpenDocumentTreeIntent();
String startDir = "Documents";
Uri uri = intent.getParcelableExtra("android.provider.extra.INITIAL_URI");
String scheme = uri.toString();
scheme = scheme.replace("/root/", "/document/");
scheme += "%3A" + startDir;
uri = Uri.parse(scheme);
Uri rootUri = DocumentsContract.buildDocumentUri(
EXTERNAL_STORAGE_PROVIDER_AUTHORITY,
uri.toString()
);
Uri treeUri = DocumentsContract.buildTreeDocumentUri(
EXTERNAL_STORAGE_PROVIDER_AUTHORITY,
uri.toString()
);
uri = Uri.parse(scheme);
Uri treeUri2 = DocumentsContract.buildTreeDocumentUri(
EXTERNAL_STORAGE_PROVIDER_AUTHORITY,
uri.toString()
);
List<Uri> uriTreeList = new ArrayList<>();
uriTreeList.add(treeUri);
uriTreeList.add(treeUri2);
getPrimaryVolume().createOpenDocumentTreeIntent()
.putExtra(EXTRA_INITIAL_URI, rootUri);
Intent intent2 = new Intent(Intent.ACTION_OPEN_DOCUMENT_TREE);
// Optionally, specify a URI for the directory that should be opened in
// the system file picker when it loads.
intent2.addFlags(
Intent.FLAG_GRANT_READ_URI_PERMISSION
| Intent.FLAG_GRANT_WRITE_URI_PERMISSION
| Intent.FLAG_GRANT_PERSISTABLE_URI_PERMISSION
| Intent.FLAG_GRANT_PREFIX_URI_PERMISSION);
intent2.putExtra(EXTRA_INITIAL_URI, rootUri);
startActivityForResult(intent2, 99);
}
})
.setCancelable(false)
.show();
}
接下来存储一些持久化权限：
@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (requestCode == 99 && resultCode == RESULT_OK) {
//get back the document tree URI (in this case we expect the documents root directory)
Uri uri = data.getData();
//now we grant permanent persistant permissions to our contentResolver and we are free to open up sub directory Uris as we please until the app is uninstalled
getSharedPreferences().edit().putString(ACCESS_FOLDER, uri.toString()).apply();
final int takeFlags = (Intent.FLAG_GRANT_READ_URI_PERMISSION | Intent.FLAG_GRANT_WRITE_URI_PERMISSION);
getApplicationContext().getContentResolver().takePersistableUriPermission(uri, takeFlags);
//simply recreate the activity although you could call some function at this point
recreate();
}
}
DocumentFile df = DocumentFile.fromTreeUri(MainActivity.this, uri);
df = df.findFile("CurrentName")
df.renameTo("NewName");
您还可以使用内容解析器打开InputStreams和OutputStreams，因为该DocumentFile的持久URI权限已授予您的内容解析器，使用以下代码片段：
getContentResolver().openInputStream(df.getUri());
getContentResolver().openOutputStream(df.getUri());
InputStreams 用于读取，OutputStreams 用于保存
您可以使用以下命令列出文件
df.listFiles();
或者您可以使用以下命令列出文件：
public static DocumentFile findFileInDirectoryMatchingName(Context mContext, Uri mUri, String name) {
final ContentResolver resolver = mContext.getContentResolver();
final Uri childrenUri = DocumentsContract.buildChildDocumentsUriUsingTree(mUri,
DocumentsContract.getDocumentId(mUri));
Cursor c = null;
try {
c = resolver.query(childrenUri, new String[]{
DocumentsContract.Document.COLUMN_DOCUMENT_ID,
DocumentsContract.Document.COLUMN_DISPLAY_NAME,
DocumentsContract.Document.COLUMN_MIME_TYPE,
DocumentsContract.Document.COLUMN_LAST_MODIFIED
}, DocumentsContract.Document.COLUMN_DISPLAY_NAME + " LIKE '?%'", new String[]{name}, null);
c.moveToFirst();
while (!c.isAfterLast()) {
final String filename = c.getString(1);
final String mimeType = c.getString(2);
final Long lastModified = c.getLong(3);
if (filename.contains(name)) {
final String documentId = c.getString(0);
final Uri documentUri = DocumentsContract.buildDocumentUriUsingTree(mUri,
documentId);
return DocumentFile.fromTreeUri(mContext, documentUri);
}
c.moveToNext();
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (c != null) {
c.close();
}
}
return null;
}
哪种方法比df.listFiles()方法运行更快
源代码（这是我自己的实现，但这里是原始的SF问题） 在针对Android 11（Api 30）时重命名视频/图像