prevent unnecessary strong referencing and controller caching

30-instruments/Project30/ImageViewController.swift

@@ -9,14 +9,16 @@
 import UIKit
 
 class ImageViewController: UIViewController {
-	var owner: SelectionViewController!
+	weak var owner: SelectionViewController!
 	var image: String!
 	var animTimer: Timer!
 
 	var imageView: UIImageView!
+    var sourceImage: UIImage!
     
     lazy var imageFilePath = Bundle.main.path(forResource: image, ofType: nil)!
-
+    lazy var imageRenderer = UIGraphicsImageRenderer(size: sourceImage.size)
+    
     
 	override func loadView() {
 		super.loadView()
@@ -52,20 +54,16 @@ class ImageViewController: UIViewController {
     override func viewDidLoad() {
         super.viewDidLoad()
         
-        guard let sourceImage = UIImage(contentsOfFile: imageFilePath) else { return }
+        sourceImage = UIImage(contentsOfFile: imageFilePath)!
 
 		title = image.replacingOccurrences(of: "-Large.jpg", with: "")
         
-		let renderer = UIGraphicsImageRenderer(size: sourceImage.size)
-
-		let roundedImage = renderer.image { ctx in
+		imageView.image = imageRenderer.image { ctx in
 			ctx.cgContext.addEllipse(in: CGRect(origin: CGPoint.zero, size: sourceImage.size))
 			ctx.cgContext.closePath()
 
 			sourceImage.draw(at: CGPoint.zero)
 		}
-
-		imageView.image = roundedImage
     }
 
 	override func viewDidAppear(_ animated: Bool) {
@@ -77,6 +75,13 @@ class ImageViewController: UIViewController {
 			self.imageView.alpha = 1
 		}
 	}
+    
+    override func viewWillDisappear(_ animated: Bool) {
+        super.viewWillDisappear(animated)
+        
+        // make the animTimer release its strong reference on this view controller
+        animTimer.invalidate()
+    }
 
 	override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
 		let defaults = UserDefaults.standard

30-instruments/Project30/SelectionViewController.swift

@@ -13,7 +13,6 @@ let cellRowHeight = 90
 
 class SelectionViewController: UITableViewController {
 	var items = [String]() // this is the array that will store the filenames to load
-	var viewControllers = [UIViewController]() // create a cache of the detail view controllers for faster loading
 	var dirty = false
     
     lazy var thumbnailRect = CGRect(origin: CGPoint.zero, size: CGSize(width: cellRowHeight, height: cellRowHeight))
@@ -106,7 +105,6 @@ class SelectionViewController: UITableViewController {
 		dirty = false
 
 		// add to our view controller cache and show
-		viewControllers.append(vc)
 		navigationController!.pushViewController(vc, animated: true)
 	}
 }