swift使用协议protocols 进行复合扩展

ViewController 增加等待指示器（菊花）

原代码

1.  
   import UIKit
2.  
    
3.  
   class BaseViewController: UIViewController {
4.  
   private let activityIndicator = UIActivityIndicatorView(style: .whiteLarge)
5.  
    
6.  
   override func viewDidLoad() {
7.  
   super.viewDidLoad()
8.  
   view.addSubview(activityIndicator)
9.  
    
10.  
    activityIndicator.translatesAutoresizingMaskIntoConstraints = false
11.  
    NSLayoutConstraint.activate([
12.  
    activityIndicator.centerXAnchor.constraint(equalTo: view.safeAreaLayoutGuide.centerXAnchor),
13.  
    activityIndicator.centerYAnchor.constraint(equalTo: view.safeAreaLayoutGuide.centerYAnchor)
14.  
    ])
15.  
    }
16.  
     
17.  
    func presenActivity() {
18.  
    activityIndicator.startAnimating()
19.  
    }
20.  
     
21.  
    func dismissActivity() {
22.  
    activityIndicator.stopAnimating()
23.  
    }
24.  
     
25.  
    func present(_ error: Error) {
26.  
    let alert = UIAlertController(title: error.localizedDescription, message: nil, preferredStyle: .alert)
27.  
    alert.addAction(.init(title: "Cancel", style: .cancel))
28.  
    present(alert, animated: true)
29.  
    }
30.  
    }

使用 protocol 拆

1.  
   protocol ActivityPresentable {
2.  
   func presentActivity()
3.  
   func dismissActivity()
4.  
   }
5.  
    
6.  
   extension ActivityPresentable where Self: UIViewController {
7.  
   func presentActivity() {
8.  
   if let activityIndicator = findActivity() {
9.  
   activityIndicator.startAnimating()
10.  
    } else {
11.  
    let activityIndicator = UIActivityIndicatorView(style: .whiteLarge)
12.  
    activityIndicator.startAnimating()
13.  
    view.addSubview(activityIndicator)
14.  
     
15.  
    activityIndicator.translatesAutoresizingMaskIntoConstraints = false
16.  
    NSLayoutConstraint.activate([
17.  
    activityIndicator.centerXAnchor.constraint(equalTo: view.safeAreaLayoutGuide.centerXAnchor),
18.  
    activityIndicator.centerYAnchor.constraint(equalTo: view.safeAreaLayoutGuide.centerYAnchor)
19.  
    ])
20.  
    }
21.  
    }
22.  
     
23.  
    func dismissActivity() {
24.  
    findActivity()?.stopAnimating()
25.  
    }
26.  
     
27.  
    func findActivity() -> UIActivityIndicatorView? {
28.  
    return view.subviews.compactMap { $0 as? UIActivityIndicatorView }.first
29.  
    }
30.  
    }

再来一个扩展

1.  
   protocol ErrorPresentable {
2.  
   func present(_ error: Error)
3.  
   }
4.  
    
5.  
   extension ErrorPresentable where Self: UIViewController {
6.  
   func present(_ error: Error) {
7.  
   let alert = UIAlertController(title: error.localizedDescription, message: nil, preferredStyle: .alert)
8.  
   alert.addAction(.init(title: "Cancel", style: .cancel))
9.  
   present(alert, animated: true)
10.  
    }
11.  
    }

使用

1.  
   class ViewController: UIViewController {
2.  
   override func viewDidLoad() {
3.  
   super.viewDidLoad()
4.  
   presentActivity()
5.  
   }
6.  
   }
7.  
    
8.  
   extension ViewController: ActivityPresentable, ErrorPresentable {}

这种方法有另外一个好处，在某些的controller里，我们可以实现自定义的ActivityIndicator

1.  
   class CustomViewController: UIViewController {
2.  
   override func viewDidLoad() {
3.  
   super.viewDidLoad()
4.  
   presentActivity()
5.  
   }
6.  
   }
7.  
    
8.  
   extension CustomViewController: ActivityPresentable {
9.  
   func presentActivity() {
10.  
    // Custom activity presenting logic
11.  
    }
12.  
     
13.  
    func dismissActivity() {
14.  
     
15.  
    }
16.  
    }

参考

https://swiftwithmajid.com/2019/01/17/using-protocols-as-composable-extensions/

官方视频：

Protocol-Oriented Programming in Swift - WWDC15 - Videos - Apple Developer

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