fix: flaky transition, wait for the transition once the target image is ready.

Author: michaelhenry

Sources/ImageViewer_swift/ImageLoader.swift

@@ -22,10 +22,8 @@ public struct URLSessionImageLoader: ImageLoader {
             }
 
             DispatchQueue.main.async {
-                UIView.setAnimationsEnabled(false)
                 imageView.image = image
                 completion(image)
-                UIView.setAnimationsEnabled(true)
             }
         }
     }

Sources/ImageViewer_swift/ImageViewerController.swift

@@ -254,7 +254,6 @@ extension ImageViewerController {
     }
 
     func updateConstraintsForSize(_ size: CGSize) {
-        
         let yOffset = max(0, (size.height - imageView.frame.height) / 2)
         top.constant = yOffset
         bottom.constant = yOffset

Sources/ImageViewer_swift/ImageViewerTransitionPresentationManager.swift

@@ -21,6 +21,8 @@ final class ImageViewerTransitionPresentationAnimator:NSObject {
 
     let isPresenting: Bool
     let imageContentMode: UIView.ContentMode
+
+    var observation: NSKeyValueObservation?
 
     init(isPresenting: Bool, imageContentMode: UIView.ContentMode) {
         self.isPresenting = isPresenting
@@ -100,10 +102,14 @@ extension ImageViewerTransitionPresentationAnimator: UIViewControllerAnimatedTra
         UIView.animate(withDuration: duration, animations: {
             dummyImageView.frame = UIScreen.main.bounds
             controller.view.alpha = 1.0
-        }) { finished in
-            transitionVC.targetView?.alpha = 1.0
-            dummyImageView.removeFromSuperview()
-            completed(finished)
+        }) { [weak self] finished in
+            self?.observation = transitionVC.targetView?.observe(\.image, options: [.new, .initial]) { img, change in
+                if img.image != nil {
+                    transitionVC.targetView?.alpha = 1.0
+                    dummyImageView.removeFromSuperview()
+                    completed(finished)
+                }
+            }
         }
     }