Storage Access Framework, takePersistableUriPermission

问题

In my application user is able to select the downloads directory. If he selects external removable SD card (not an emulated sd card!, but a memory, which is a real physicel microSD card for example), starting from Android 4.4 I am only able to write to it using SAF (Storage Access Framework).

I've figured out how to create and write a single file using SAF:

public void newFile() {
    Intent intent = new Intent(Intent.ACTION_CREATE_DOCUMENT);

    intent.addCategory(Intent.CATEGORY_OPENABLE);
    intent.setType("text/plain");
    intent.putExtra(Intent.EXTRA_TITLE, "newfile.txt");

    startActivityForResult(intent, CREATE_REQUEST_CODE);
}

public void saveFile() {
    Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT);
    intent.addCategory(Intent.CATEGORY_OPENABLE);
    intent.setType("text/plain");

    startActivityForResult(intent, SAVE_REQUEST_CODE);
}

And here is my onActivityResult, where I actually write to file:

public void onActivityResult(int requestCode, int resultCode,
                             Intent resultData) {
    Uri currentUri = null;

    if (resultCode == Activity.RESULT_OK) {
        if (requestCode == CREATE_REQUEST_CODE) {
            if (resultData != null) {
                Log.d(TAG, "CREATE_REQUEST_CODE resultData = " + resultData);
            }
        } else if (requestCode == SAVE_REQUEST_CODE) {

            if (resultData != null) {
                currentUri = resultData.getData();
                getContentResolver().takePersistableUriPermission(currentUri, Intent.FLAG_GRANT_READ_URI_PERMISSION
                        | Intent.FLAG_GRANT_WRITE_URI_PERMISSION);
                writeFileContent(currentUri);
                Log.d(TAG, "SAVE_REQUEST_CODE currentUri = " + currentUri);
            }
        }
    }
}

And also writeFileContent:

private void writeFileContent(Uri uri) {
    try {
        ParcelFileDescriptor pfd =
                this.getContentResolver().
                        openFileDescriptor(uri, "w");

        FileOutputStream fileOutputStream =
                new FileOutputStream(pfd.getFileDescriptor());

        String textContent = "some text";

        fileOutputStream.write(textContent.getBytes());

        fileOutputStream.close();
        pfd.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

And finally my question:

How do I create other files, and write them after I called getContentResolver().takePersistableUriPermission without a prompt to select a directory in future?

If I'm right, then getContentResolver().takePersistableUriPermission shoudl allow me to do tha

回答1:

Thanks to @earthw0rmjim answer, and googling, I figgured out a complete solution:

public void saveFile() {
    List<UriPermission> permissions = getContentResolver().getPersistedUriPermissions();
    if (permissions != null && permissions.size() > 0) {
        DocumentFile pickedDir = DocumentFile.fromTreeUri(this, permissions.get(0).getUri());
        DocumentFile file = pickedDir.createFile("text/plain", "try2.txt");
        writeFileContent(file.getUri());
    } else {
        Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT);
        intent.addCategory(Intent.CATEGORY_OPENABLE);
        intent.setType("text/plain");

        startActivityForResult(intent, SAVE_REQUEST_CODE);
    }
}

So firstly, if we don't have PersistedUriPermissions, it will request such permissions. This way here is how onActivityResult looks like

public void onActivityResult(int requestCode, int resultCode,
                             Intent resultData) {
    Uri currentUri = null;

    if (resultCode == Activity.RESULT_OK) {
        if (requestCode == SELECT_DIR_REQUEST_CODE) {
            if (resultData != null) {
                Uri treeUri=resultData.getData();
                Log.d(TAG, "SELECT_DIR_REQUEST_CODE resultData = " + resultData);
                getContentResolver().takePersistableUriPermission(treeUri, Intent.FLAG_GRANT_READ_URI_PERMISSION
                        | Intent.FLAG_GRANT_WRITE_URI_PERMISSION);
                DocumentFile pickedDir = DocumentFile.fromTreeUri(this, treeUri);
                DocumentFile file = pickedDir.createFile("text/plain", "try2.txt");
                writeFileContent(file.getUri());
            }
        }
    }
}

And the writeFileContent looks same as in the question

private void writeFileContent(Uri uri) {
    try {
        ParcelFileDescriptor pfd =
                this.getContentResolver().
                        openFileDescriptor(uri, "w");

        FileOutputStream fileOutputStream =
                new FileOutputStream(pfd.getFileDescriptor());

        String textContent = "some text";

        fileOutputStream.write(textContent.getBytes());

        fileOutputStream.close();
        pfd.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

来源：https://stackoverflow.com/questions/40172011/storage-access-framework-takepersistableuripermission