How to make an asynchronous Dart call synchronous?

The only time that you can wrap an async method in a synchronous one is when you don’t need to get a return value.

For example if you want to disable the save button, save results to the server asynchronously and re-enable the save button when the job is done you can write it like this:

Future<bool> save() async {
  // save changes async here
  return true;
}

void saveClicked() {
  saveButton.enabled = false;
  save()
    .then((success) => window.alert(success ? 'Saved' : 'Failed'))
    .catchError((e) => window.alert(e))
    .whenComplete(() { saveButton.enabled = true; });
}

Note that the saveClicked method is fully synchronous, but executes the save method asynchronously.

Note that if you make saveClicked async, not only do you have to call it using the async pattern, but the entire method body will run asynchronously so the save button will not be disabled when the function returns.

For completeness the async version of saveClicked looks like this:

Future<Null> saveClicked() async {
  saveButton.enabled = false;
  try {
    bool success = await save();
    window.alert(success ? 'Saved' : 'Failed');
  }
  catch (e) {
    window.alert(e);
  }
  finally {
    saveButton.enabled = true;
  }
}