[SwiftUI] Adds forcesEarlySwiftUIRendering flag to fix SwiftUI Cell S…

…izing (#153)

* [SwiftUI] Fix reused UIHostingController sizing

* Added to collection view configuration

---------

Co-authored-by: michael gofron <[email protected]>

CHANGELOG.md

@@ -17,6 +17,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   batch update.
 - Added caching for `visibilityMetadata` calculations.
 - Fixed an issue that could cause SwiftUI views to be incorrectly sized in a collection view.
+- Added `forcesEarlySwiftUIRendering` flag to `CollectionViewConfiguration` to test a SwiftUI layout
+  approach to resolve an issue that could cause collection view cells to layout with 
+  unexpected dimensions
 
 ## [0.10.0](https://github.com/airbnb/epoxy-ios/compare/0.9.0...0.10.0) - 2023-06-29
 

Sources/EpoxyCollectionView/CollectionView/CollectionView.swift

@@ -445,6 +445,7 @@ open class CollectionView: UICollectionView {
     }
 
     cell.itemPath = itemPath
+    cell.forcesEarlySwiftUIRendering = configuration.forcesEarlySwiftUIRendering
 
     let metadata = ItemCellMetadata(
       traitCollection: traitCollection,
@@ -469,6 +470,7 @@ open class CollectionView: UICollectionView {
     animated: Bool)
   {
     supplementaryView.itemPath = itemPath
+    supplementaryView.forcesEarlySwiftUIRendering = configuration.forcesEarlySwiftUIRendering
     model.configure(
       reusableView: supplementaryView,
       traitCollection: traitCollection,

Sources/EpoxyCollectionView/CollectionView/CollectionViewConfiguration.swift

@@ -13,11 +13,13 @@ public struct CollectionViewConfiguration {
   public init(
     usesBatchUpdatesForAllReloads: Bool = true,
     usesCellPrefetching: Bool = true,
-    usesAccurateScrollToItem: Bool = true)
+    usesAccurateScrollToItem: Bool = true,
+    forcesEarlySwiftUIRendering: Bool = true)
   {
     self.usesBatchUpdatesForAllReloads = usesBatchUpdatesForAllReloads
     self.usesCellPrefetching = usesCellPrefetching
     self.usesAccurateScrollToItem = usesAccurateScrollToItem
+    self.forcesEarlySwiftUIRendering = forcesEarlySwiftUIRendering
   }
 
   // MARK: Public
@@ -66,4 +68,10 @@ public struct CollectionViewConfiguration {
   ///
   /// - SeeAlso: `CollectionViewScrollToItemHelper`
   public var usesAccurateScrollToItem: Bool
+
+  /// Flag to use a semi-private API to force an early render of a SwiftUI view embedded in a `UIHostingController`. This is used
+  /// to synchronously resize after updating the `rootView`. When disabled, layout is forced using standard UIKit functions, a newer
+  /// approach which is being tested for viability and to resolve issues where SwiftUI views in collection view cells undergo a layout pass
+  /// with unexpected dimensions.
+  public var forcesEarlySwiftUIRendering: Bool
 }

Sources/EpoxyCollectionView/CollectionView/ReusableViews/CollectionViewCell.swift

@@ -7,7 +7,7 @@ import UIKit
 // MARK: - CollectionViewCell
 
 /// An internal cell class for use in a `CollectionView`.
-public final class CollectionViewCell: UICollectionViewCell, ItemCellView {
+public final class CollectionViewCell: UICollectionViewCell, ItemCellView, SwiftUIRenderingConfigurable {
 
   // MARK: Lifecycle
 
@@ -27,6 +27,13 @@ public final class CollectionViewCell: UICollectionViewCell, ItemCellView {
 
   public var selectedBackgroundColor: UIColor?
 
+  /// See `CollectionViewConfiguration.forcesEarlySwiftUIRendering` for an explanation of this behavior.
+  public var forcesEarlySwiftUIRendering = true {
+    didSet {
+      updateForcesEarlySwiftUIRendering()
+    }
+  }
+
   override public var isSelected: Bool {
     didSet {
       updateVisualHighlightState(isSelected)
@@ -59,6 +66,8 @@ public final class CollectionViewCell: UICollectionViewCell, ItemCellView {
       view.topAnchor.constraint(equalTo: contentView.topAnchor),
       view.bottomAnchor.constraint(equalTo: contentView.bottomAnchor),
     ])
+
+    updateForcesEarlySwiftUIRendering()
   }
 
   override public func preferredLayoutAttributesFitting(
@@ -152,6 +161,12 @@ public final class CollectionViewCell: UICollectionViewCell, ItemCellView {
     }
   }
 
+  private func updateForcesEarlySwiftUIRendering() {
+    if let configurableView = view as? SwiftUIRenderingConfigurable {
+      configurableView.forcesEarlySwiftUIRendering = forcesEarlySwiftUIRendering
+    }
+  }
+
 }
 
 // MARK: EphemeralCachedStateView

Sources/EpoxyCollectionView/CollectionView/ReusableViews/CollectionViewReusableView.swift

@@ -1,10 +1,11 @@
 //  Created by Laura Skelton on 9/8/17.
 //  Copyright © 2017 Airbnb. All rights reserved.
 
+import EpoxyCore
 import UIKit
 
 /// An internal collection reusable view class for use in a `CollectionView`.
-public final class CollectionViewReusableView: UICollectionReusableView {
+public final class CollectionViewReusableView: UICollectionReusableView, SwiftUIRenderingConfigurable {
 
   // MARK: Lifecycle
 
@@ -22,6 +23,13 @@ public final class CollectionViewReusableView: UICollectionReusableView {
 
   public private(set) var view: UIView?
 
+  /// See `CollectionViewConfiguration.forcesEarlySwiftUIRendering` for an explanation of this behavior.
+  public var forcesEarlySwiftUIRendering = false {
+    didSet {
+      updateForcesEarlySwiftUIRendering()
+    }
+  }
+
   /// Pass a view for this view's element kind and reuseID that the view will pin to its edges.
   public func setViewIfNeeded(view: UIView) {
     if self.view != nil {
@@ -39,6 +47,8 @@ public final class CollectionViewReusableView: UICollectionReusableView {
       view.bottomAnchor.constraint(equalTo: bottomAnchor),
     ])
     self.view = view
+
+    updateForcesEarlySwiftUIRendering()
   }
 
   override public func preferredLayoutAttributesFitting(
@@ -76,4 +86,12 @@ public final class CollectionViewReusableView: UICollectionReusableView {
   /// post-update data.
   var itemPath: SupplementaryItemPath?
 
+  // MARK: Private
+
+  private func updateForcesEarlySwiftUIRendering() {
+    if let configurableView = view as? SwiftUIRenderingConfigurable {
+      configurableView.forcesEarlySwiftUIRendering = forcesEarlySwiftUIRendering
+    }
+  }
+
 }

Sources/EpoxyCore/SwiftUI/EpoxySwiftUIHostingView.swift

@@ -57,7 +57,7 @@ extension CallbackContextEpoxyModeled
 /// the API is private and 3) the `_UIHostingView` doesn't not accept setting a new `View` instance.
 ///
 /// - SeeAlso: `EpoxySwiftUIHostingController`
-public final class EpoxySwiftUIHostingView<RootView: View>: UIView, EpoxyableView {
+public final class EpoxySwiftUIHostingView<RootView: View>: UIView, EpoxyableView, SwiftUIRenderingConfigurable {
 
   // MARK: Lifecycle
 
@@ -130,6 +130,9 @@ public final class EpoxySwiftUIHostingView<RootView: View>: UIView, EpoxyableVie
     }
   }
 
+  /// See `CollectionViewConfiguration.forcesEarlySwiftUIRendering` for an explanation of this behavior.
+  public var forcesEarlySwiftUIRendering = true
+
   public override func didMoveToWindow() {
     super.didMoveToWindow()
 
@@ -183,12 +186,18 @@ public final class EpoxySwiftUIHostingView<RootView: View>: UIView, EpoxyableVie
     // The view controller must be added to the view controller hierarchy to measure its content.
     addViewControllerIfNeededAndReady()
 
-    // As of iOS 15.2, `UIHostingController` now renders updated content asynchronously, and as such
-    // this view will get sized incorrectly with the previous content when reused unless we invoke
-    // this semi-private API. We couldn't find any other method to get the view to resize
-    // synchronously after updating `rootView`, but hopefully this will become a public API soon so
-    // we can remove this call.
-    viewController._render(seconds: 0)
+    if forcesEarlySwiftUIRendering {
+      // As of iOS 15.2, `UIHostingController` now renders updated content asynchronously, and as such
+      // this view will get sized incorrectly with the previous content when reused unless we invoke
+      // this semi-private API. We couldn't find any other method to get the view to resize
+      // synchronously after updating `rootView`, but hopefully this will become a public API soon so
+      // we can remove this call.
+      viewController._render(seconds: 0)
+    } else {
+      // We need to layout the view to ensure it gets resized properly when cells are re-used
+      viewController.view.setNeedsLayout()
+      viewController.view.layoutIfNeeded()
+    }
 
     // This is required to ensure that views with new content are properly resized.
     viewController.view.invalidateIntrinsicContentSize()
@@ -343,10 +352,6 @@ public final class EpoxySwiftUIHostingView<RootView: View>: UIView, EpoxyableVie
 
     addSubview(viewController.view)
 
-    // Get the view controller's view to be sized correctly so that we don't have to wait for
-    // autolayout to perform a pass to do so.
-    viewController.view.frame = bounds
-
     viewController.view.translatesAutoresizingMaskIntoConstraints = false
     NSLayoutConstraint.activate([
       viewController.view.leadingAnchor.constraint(equalTo: leadingAnchor),
@@ -432,3 +437,10 @@ struct EpoxyHostingWrapper<Content: View>: View {
 }
 
 #endif
+
+// MARK: - SwiftUIRenderingConfigurable
+
+public protocol SwiftUIRenderingConfigurable: AnyObject {
+  /// See `CollectionViewConfiguration.forcesEarlySwiftUIRendering` for an explanation of this behavior.
+  var forcesEarlySwiftUIRendering: Bool { get set }
+}