以面向协议的方式实施活动指示器

Question

我想创建协议，当它们符合此协议时，它将使我能够向UIViewController及其子类添加活动指示符/从UIViewController及其子类中移除活动指示符。

所以我最终得到了这样的代码

protocol ActivityIndicatorPresenter {
    var activityIndicator: UIActivityIndicatorView { get }
    func showActivityIndicator()
    func hideActivityIndicator()
}

extension ActivityIndicatorPresenter where Self: UIViewController {
    func showActivityIndicator() {
        dispatch_async(dispatch_get_main_queue()) {
            self.activityIndicator.color = UIColor.blackColor()
            self.activityIndicator.frame = CGRect(x: 0.0, y: 0.0, width: 80.0, height: 80.0)
            self.activityIndicator.center = CGPoint(x:self.view.bounds.size.width / 2, y:self.view.bounds.size.height / 2)
            self.view.addSubview(self.activityIndicator)
            self.activityIndicator.startAnimating()
    }
}

    func hideActivityIndicator() {
        dispatch_async(dispatch_get_main_queue()) {
            self.activityIndicator.stopAnimating()
            self.activityIndicator.removeFromSuperview()
        }
    }
}

并在UIViewController的子类中：

class MyViewController: ActivityIndicatorPresenter {
    var activityIndicator: UIActivityIndicator { get {return self.spinner}}
    var spinner = UIActivityIndicator()
}

一切正常，但我认为在计算属性的getter中返回存储的属性是一种解决方法。是更漂亮的实现方式吗？