getTmpFile function
写入一个临时文件
Implementation
Future<File?> getTmpFile(
Uint8List? bytes, {
required Directory dir,
String ext = '',
}) async {
if (bytes == null) return null;
final file = File('${dir.path}/${const Uuid().v4()}${ext.prefixWith('.')}');
await file.writeAsBytes(bytes);
return file;
}