iOS动态更换Icon的全过程记录

// If false, alternate icons are not supported for the current process.
@available(iOS 10.3, *)
open var supportsAlternateIcons: Bool { get }
  
// Pass `nil` to use the primary application icon. The completion handler will be invoked asynchronously on an arbitrary background queue; be sure to dispatch back to the main queue before doing any further UI work.
@available(iOS 10.3, *)
open func setAlternateIconName(_ alternateIconName: String?, completionHandler: ((Error?) -> Void)? = nil)
  
// If `nil`, the primary application icon is being used.
@available(iOS 10.3, *)
open var alternateIconName: String? { get }

@IBAction func changeOneClick(_ sender: Any) {
  if UIApplication.shared.supportsAlternateIcons {
    UIApplication.shared.setAlternateIconName("lambot") { (error) in
      if error != nil {
        print("更换icon错误")
      }
    }
  }
}

@IBAction func resetClick(_ sender: Any) {
  if UIApplication.shared.supportsAlternateIcons {
    UIApplication.shared.setAlternateIconName(nil) { (error) in
      if error != nil {
        print("更换icon错误")
      }
    }
  }
}

extension UIViewController {
  public class func initializeMethod() {
    if self != UIViewController.self {
      return
    }
		// Method Swizzling
    DispatchQueue.once(token: "ChangeIcon") {
      let orignal = class_getInstanceMethod(self, #selector(UIViewController.present(_:animated:completion:)))
      let swizzling = class_getInstanceMethod(self, #selector(UIViewController.jt_present(_:animated:completion:)))

      if let old = orignal, let new = swizzling {
        method_exchangeImplementations(old, new)
      }
    }
  }

  @objc private func jt_present(_ viewControllerToPresent: UIViewController, animated flag: Bool, completion: (() -> Void)? = nil) {
    // 在这里判断是否是更换icon时的弹出框
    if viewControllerToPresent is UIAlertController {

      let alertTitle = (viewControllerToPresent as! UIAlertController).title
      let alertMessage = (viewControllerToPresent as! UIAlertController).message

      // 更换icon时的弹出框，这两个string都为nil。
      if alertTitle == nil && alertMessage == nil {
        return
      }
    }
		
		// 因为方法已经交换，这个地方的调用就相当于调用原先系统的 present
    self.jt_present(viewControllerToPresent, animated: flag, completion: completion)
  }
}

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {

  UIViewController.initializeMethod()

  return true
}

extension DispatchQueue {
  private static var _onceTracker = [String]()
  public class func once(token: String, block: () -> ()) {
    objc_sync_enter(self)
    defer {
      objc_sync_exit(self)
    }
    if _onceTracker.contains(token) {
      return
    }
    _onceTracker.append(token)
    block()
  }
}