在使用ACTION_OPEN_DOCUMENT_TREE打开时，需要调用许可请求并获得授权后，才能使用该目录下的所有文件和文件夹。在选择目录时，需要保证选择的目录是存储卡的顶级目录，而不是子目录。在获取树权限后，需要使用Uri获取该目录的访问权限，并在代码中进行访问控制。

以下是示例代码：

fun requestStoragePermission(activity: Activity, requestCode: Int) {
   val storagePermission = Manifest.permission.WRITE_EXTERNAL_STORAGE
   if (ContextCompat.checkSelfPermission(activity, storagePermission) != PackageManager.PERMISSION_GRANTED) {
       ActivityCompat.requestPermissions(activity, arrayOf(storagePermission), requestCode)
   }
}

val REQUEST_CODE_OPEN_DOCUMENT_TREE = 1
val EXPORT_FOLDER_NAME = "Exported Files"
 
fun createFile() {
   val intent = Intent(Intent.ACTION_OPEN_DOCUMENT_TREE).apply {
       flags = Intent.FLAG_GRANT_WRITE_URI_PERMISSION or Intent.FLAG_GRANT_READ_URI_PERMISSION or Intent.FLAG_GRANT_PERSISTABLE_URI_PERMISSION
   }
   startActivityForResult(intent, REQUEST_CODE_OPEN_DOCUMENT_TREE)
}
 
override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
   if (requestCode == REQUEST_CODE_OPEN_DOCUMENT_TREE && resultCode == RESULT_OK) {
       data?.data?.also { uri ->
           val folderName = EXPORT_FOLDER_NAME
           val directory = DocumentsContract.getTreeDocumentId(uri)
           val documentUri = DocumentsContract.buildDocumentUriUsingTree(uri, directory)
           val folderUri = DocumentsContract.createDocument(contentResolver, documentUri, DocumentsContract.Document.MIME_TYPE_DIR, folderName)
           val fileUri = DocumentsContract.createDocument(contentResolver, folderUri, "text/plain", "example.txt")
           contentResolver.openFileDescriptor(fileUri, "w")?.use {
               FileOutputStream(it.fileDescriptor).use { output ->
                   val text = "Hello world!"
                   output.write(text.toByteArray())
                   output.flush()
               }
           }
           revokeUriPermission(fileUri, Intent.FLAG_GRANT_WRITE_URI_PERMISSION or Intent.FLAG_GRANT_READ_URI_PERMISSION)
       }
   }
}