Release cell reference on prepareForReuse as a fix for iOS 15+ cell…

… lifecycle changes. On iOS 15+, for performance reasons, the table view data source may create cells ahead of time using the `cellForRow` method. So the cell may be created but never go through the whole `willDisplayCell/didEndDisplaying` lifecycle callbacks as it may never be displayed. However, we start loading the cell image on `cellForRow` and only cancel the request on `didEndDisplaying`. In such cases, there can be a race condition when reusing a cell that was never displayed because the request would carry on and potentially load the wrong image at the wrong index path.

EssentialApp/EssentialAppTests/FeedUIIntegrationTests.swift

@@ -492,6 +492,21 @@ class FeedUIIntegrationTests: XCTestCase {
 		XCTAssertEqual(view0?.isShowingImageLoadingIndicator, false, "Expected no loading indicator when image loads successfully after view becomes visible again")
 	}
 
+	func test_feedImageView_doesNotShowDataFromPreviousRequestWhenCellIsReused() throws {
+		let (sut, loader) = makeSUT()
+
+		sut.loadViewIfNeeded()
+		loader.completeFeedLoading(with: [makeImage(), makeImage()])
+
+		let view0 = try XCTUnwrap(sut.simulateFeedImageViewVisible(at: 0))
+		view0.prepareForReuse()
+
+		let imageData0 = UIImage.make(withColor: .red).pngData()!
+		loader.completeImageLoading(with: imageData0, at: 0)
+
+		XCTAssertEqual(view0.renderedImage, .none, "Expected no image state change for reused view once image loading completes successfully")
+	}
+
 	func test_feedImageView_doesNotRenderLoadedImageWhenNotVisibleAnymore() {
 		let (sut, loader) = makeSUT()
 		sut.loadViewIfNeeded()

EssentialFeed/EssentialFeediOS/Feed UI/Controllers/FeedImageCellController.swift

@@ -42,6 +42,9 @@ extension FeedImageCellController: UITableViewDataSource, UITableViewDelegate, U
 		cell?.onRetry = { [weak self] in
 			self?.delegate.didRequestImage()
 		}
+		cell?.onReuse = { [weak self] in
+			self?.releaseCellForReuse()
+		}
 		delegate.didRequestImage()
 		return cell!
 	}

EssentialFeed/EssentialFeediOS/Feed UI/Views/FeedImageCell.swift

@@ -13,8 +13,15 @@ public final class FeedImageCell: UITableViewCell {
 	@IBOutlet private(set) public var descriptionLabel: UILabel!
 
 	var onRetry: (() -> Void)?
+	var onReuse: (() -> Void)?
 
 	@IBAction private func retryButtonTapped() {
 		onRetry?()
 	}
+
+	public override func prepareForReuse() {
+		super.prepareForReuse()
+
+		onReuse?()
+	}
 }