Set transparentAttributeWhenCellNotLoaded to false by default and add a SwiftUI modifier for that

Author: amirdew

Lib/CollectionViewPagingLayout.swift

@@ -38,8 +38,8 @@ public class CollectionViewPagingLayout: UICollectionViewLayout {
     /// See `ZPositionHandler` for details
     public var zPositionHandler: ZPositionHandler = .both
 
-    /// Set `alpha` to zero when the cell is not loaded yet by collection view
-    public var transparentAttributeWhenCellNotLoaded: Bool = true
+    /// Set `alpha` to zero when the cell is not loaded yet by collection view, enabling this prevents showing a cell before applying transforms but may cause flashing when you reload the data
+    public var transparentAttributeWhenCellNotLoaded: Bool = false
 
     /// The animator for setting `contentOffset`
     ///

Lib/SwiftUI/PagingCollectionViewController.swift

@@ -57,13 +57,12 @@ public class PagingCollectionViewController<ValueType: Identifiable, PageContent
     // MARK: Internal functions
 
     func update(list: [ValueType], currentIndex: Int?) {
-        if needsToReloadData(list: list) {
-            collectionView.performBatchUpdates({
-                collectionView.reloadData()
-                layout.invalidateLayoutInBatchUpdate()
-            })
-        }
+        let oldIds = self.list.map(\.id)
         self.list = list
+        if list.map(\.id) != oldIds {
+            collectionView?.reloadData()
+            layout.invalidateLayoutInBatchUpdate(invalidateOffset: true)
+        }
         let index = currentIndex ?? layout.currentPage
         if index < list.count {
             guard index != layout.currentPage else { return }
@@ -88,11 +87,7 @@ public class PagingCollectionViewController<ValueType: Identifiable, PageContent
 
 
     // MARK: Private functions
-
-    private func needsToReloadData(list: [ValueType]) -> Bool {
-        self.list.map(\.id) != list.map(\.id)
-    }
-
+    
     private func setupCollectionView() {
         collectionView = UICollectionView(
             frame: view.frame,
@@ -106,6 +101,7 @@ public class PagingCollectionViewController<ValueType: Identifiable, PageContent
         layout.numberOfVisibleItems = modifierData?.numberOfVisibleItems
         layout.scrollDirection = modifierData?.scrollDirection ?? layout.scrollDirection
         layout.defaultAnimator = modifierData?.animator
+        layout.transparentAttributeWhenCellNotLoaded = modifierData?.transparentAttributeWhenCellNotLoaded ?? layout.transparentAttributeWhenCellNotLoaded
         collectionView.delegate = self
 
         collectionView.showsHorizontalScrollIndicator = false

Lib/SwiftUI/PagingCollectionViewModifierData.swift

@@ -25,6 +25,7 @@ struct PagingCollectionViewModifierData {
     var onTapPage: ((Int) -> Void)?
     var scrollDirection: UICollectionView.ScrollDirection?
     var pagePadding: PagePadding?
+    var transparentAttributeWhenCellNotLoaded: Bool?
 }
 
 @available(iOS 13.0, *)

Lib/SwiftUI/TransformPageViewProtocol.swift

@@ -86,6 +86,11 @@ public extension TransformPageViewProtocol {
         return self
     }
 
+    func hideCellWhenNotLoaded(_ value: Bool) -> Self {
+        self.builder.modifierData.transparentAttributeWhenCellNotLoaded = value
+        return self
+    }
+
     func collectionView<T>(_ key: WritableKeyPath<UICollectionView, T>, _ value: T) -> Self {
         let property = CollectionViewProperty(keyPath: key, value: value)
         self.builder.modifierData.collectionViewProperties.append(property)

Samples/PagingLayoutSamples/Modules/UIKit/Cards/CardsViewController.swift

@@ -81,6 +81,7 @@ class CardsViewController: UIViewController, NibBased, ViewModelBased {
         collectionView.dataSource = self
         layout.numberOfVisibleItems = 7
         layout.scrollDirection = .vertical
+        layout.transparentAttributeWhenCellNotLoaded = true
         collectionView.collectionViewLayout = layout
         collectionView.showsVerticalScrollIndicator = false
         collectionView.clipsToBounds = false

Samples/PagingLayoutSamples/Modules/UIKit/Shapes/ShapesViewController.swift

@@ -111,7 +111,6 @@ class ShapesViewController: UIViewController, NibBased, ViewModelBased {
         collectionView.isPagingEnabled = true
         collectionView.dataSource = self
         let layout = CollectionViewPagingLayout()
-        layout.transparentAttributeWhenCellNotLoaded = false
         collectionView.collectionViewLayout = layout
         layout.delegate = self
         collectionView.showsHorizontalScrollIndicator = false