pickImage method
Implementation
Future<void> pickImage() async => await FilePicker.platform.pickFiles(
type : FileType.custom,
allowedExtensions : _fileTypes,
lockParentWindow : true
).then((response) async {
if (response != null) {
_file = response.files.single;
_extension = _file!.extension??'';
_hasImage = true;
}
notifyListeners();
});