Android 9无法在Android外部公共路径内创建目录(“storage/emulated/0/MyImages”)

Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT_TREE);
startActivityForResult(intent, REQUEST_CODE);

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (requestCode == REQUEST_CODE && resultCode == RESULT_OK) {
        Uri treeUri = data.getData();
        DocumentFile pickedDir = DocumentFile.fromTreeUri(this, treeUri);
        createDirectory(pickedDir, "MyImages");
    }
}

private void createDirectory(DocumentFile parentDir, String dirName) {
    DocumentFile newDir = parentDir.createDirectory(dirName);
    if (newDir != null) {
        // 目录创建成功
    } else {
        // 目录创建失败
    }
}