Prevent the demo from crashing

The button is now disabled when animation is completed

Playground/RxSwiftExtPlayground.playground/Pages/UIViewPropertyAnimator+Rx.xcplaygroundpage/Contents.swift

@@ -1,6 +1,6 @@
 /*:
  > # IMPORTANT: To use `RxSwiftExtPlayground.playground`, please:
-
+ 
  1. Make sure you have [Carthage](https://github.com/Carthage/Carthage) installed
  1. Fetch Carthage dependencies from shell: `carthage bootstrap --platform ios`
  1. Build scheme `RxSwiftExtPlayground` scheme for a simulator target
@@ -17,82 +17,85 @@ import UIKit
 
 /*:
  ## animate
-
+ 
  The `animate` operator provides a Completable that triggers the animation upon subscription and completes when the animation ends.
-
+ 
  Please open the Assistant Editor (⌘⌥⏎) to see the Interactive Live View example.
  */
 
 class AnimateViewController: UIViewController {
-
+    
     let disposeBag = DisposeBag()
-
+    
     lazy var box1: UIView = {
         let view = UIView(frame: CGRect(x: 100, y: 100, width: 100, height: 100))
         view.backgroundColor = .red
         return view
     }()
-
+    
     lazy var box2: UIView = {
         let view = UIView(frame: CGRect(x: 100, y: 220, width: 100, height: 100))
         view.backgroundColor = .green
         return view
     }()
-
+    
     lazy var box3: UIView = {
         let view = UIView(frame: CGRect(x: 100, y: 340, width: 100, height: 100))
         view.backgroundColor = .blue
         return view
     }()
-
+    
     lazy var button: UIButton = {
         let button = UIButton(frame: CGRect(x: 100, y: 500, width: 200, height: 50))
         button.setTitle("Play animation", for: .normal)
         button.setTitleColor(.blue, for: .normal)
         button.backgroundColor = .white
         button.layer.borderColor = UIColor.black.cgColor
         button.layer.borderWidth = 2
-
+        
         return button
     }()
-
+    
     lazy var animator1 = {
         UIViewPropertyAnimator(duration: 0.3, curve: .easeInOut) { [unowned self] in
             self.box1.transform = CGAffineTransform(translationX: 0, y: -100)
         }
     }()
-
+    
     lazy var animator2 = {
         UIViewPropertyAnimator(duration: 0.25, curve: .easeInOut) { [unowned self] in
             self.box2.transform = CGAffineTransform(translationX: 0, y: -100)
-                                    .scaledBy(x: 1.2, y: 1.2)
+                .scaledBy(x: 1.2, y: 1.2)
         }
     }()
-
+    
     lazy var animator3 = {
         UIViewPropertyAnimator(duration: 0.15, curve: .easeInOut) { [unowned self] in
             self.box3.transform = CGAffineTransform(translationX: 0, y: -100)
-                                    .rotated(by: CGFloat(M_PI))
+                .rotated(by: CGFloat(M_PI))
         }
     }()
-
+    
     override func viewDidLoad() {
         super.viewDidLoad()
-
+        
         // construct the main view
         let views = [box1, box2, box3, button]
         view.backgroundColor = .white
-
+        
         views.forEach {
             view.addSubview($0)
         }
-
+        
         // Trigger chained animations after a button tap
         button.rx.tap
             .flatMap { [unowned self] in
                 self.animator1.rx.animate()
                     .andThen(self.animator2.rx.animate(afterDelay: 0.2))
                     .andThen(self.animator3.rx.animate(afterDelay: 0.1))
+                    .do(onCompleted: { [unowned self] in
+                        self.button.isEnabled = false
+                    })
                     .debug("animation sequence")
             }
             .subscribe()