compute() {
    let actions = [];
    each(this.manager.recognizers, (recognizer) => {
      if (boolOrFn(recognizer.options.enable, [recognizer])) {
        actions = actions.concat(recognizer.getTouchAction());
      }
    });
    return cleanTouchActions(actions.join(' '));
  }
@private
compute the value for the touchAction property based on the recognizer's settings
@returns {String} value