use custom 'PagerData' protocol for data to avoid unexpected slowness

Example/SwiftUIPagerExample.xcodeproj/project.pbxproj

@@ -15,6 +15,7 @@
 		17D9E0F823D4CF6700C5AE93 /* ContentView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 17D9E0F723D4CF6700C5AE93 /* ContentView.swift */; };
 		17D9E0FD23D4CF6900C5AE93 /* Assets.xcassets in Resources */ = {isa = PBXBuildFile; fileRef = 17D9E0FC23D4CF6900C5AE93 /* Assets.xcassets */; };
 		17D9E10023D4CF6900C5AE93 /* LaunchScreen.storyboard in Resources */ = {isa = PBXBuildFile; fileRef = 17D9E0FE23D4CF6900C5AE93 /* LaunchScreen.storyboard */; };
+		576BF5CC28E0CAAA00E73618 /* PagerData.swift in Sources */ = {isa = PBXBuildFile; fileRef = 576BF5CB28E0CAAA00E73618 /* PagerData.swift */; };
 		6B22DC81247E5C9A00EF95C5 /* NestedExampleView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 6B22DC80247E5C9A00EF95C5 /* NestedExampleView.swift */; };
 		6B35B6C125346610000D618F /* PaginationSensitivity.swift in Sources */ = {isa = PBXBuildFile; fileRef = 6B35B6C025346610000D618F /* PaginationSensitivity.swift */; };
 		6B4EC8A2240D072B001E7490 /* ColorsExampleView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 6B4EC8A1240D072B001E7490 /* ColorsExampleView.swift */; };
@@ -63,6 +64,7 @@
 		17D9E0FC23D4CF6900C5AE93 /* Assets.xcassets */ = {isa = PBXFileReference; lastKnownFileType = folder.assetcatalog; name = Assets.xcassets; path = ../Assets.xcassets; sourceTree = "<group>"; };
 		17D9E0FF23D4CF6900C5AE93 /* Base */ = {isa = PBXFileReference; lastKnownFileType = file.storyboard; name = Base; path = Base.lproj/LaunchScreen.storyboard; sourceTree = "<group>"; };
 		17D9E10123D4CF6900C5AE93 /* Info.plist */ = {isa = PBXFileReference; lastKnownFileType = text.plist.xml; path = Info.plist; sourceTree = "<group>"; };
+		576BF5CB28E0CAAA00E73618 /* PagerData.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; name = PagerData.swift; path = ../../Sources/SwiftUIPager/PagerData.swift; sourceTree = "<group>"; };
 		6B22DC80247E5C9A00EF95C5 /* NestedExampleView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = NestedExampleView.swift; sourceTree = "<group>"; };
 		6B35B6C025346610000D618F /* PaginationSensitivity.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; name = PaginationSensitivity.swift; path = ../../Sources/SwiftUIPager/PageConfiguration/PaginationSensitivity.swift; sourceTree = "<group>"; };
 		6B4EC8A1240D072B001E7490 /* ColorsExampleView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ColorsExampleView.swift; sourceTree = "<group>"; };
@@ -162,6 +164,7 @@
 				6BC5EDFB24866D9500E1E78C /* PagerContent+Helper.swift */,
 				6BEF676F24C98B62008533FE /* PageWrapper.swift */,
 				1748E8BF26695E220016F534 /* PageTransition.swift */,
+				576BF5CB28E0CAAA00E73618 /* PagerData.swift */,
 			);
 			name = Pagination;
 			sourceTree = "<group>";
@@ -294,6 +297,7 @@
 				6BCF139224B2677B00AADE74 /* ContentLoadingPolicy.swift in Sources */,
 				6BEA731524ACF8D7007EA8DC /* SwipeInteractionArea.swift in Sources */,
 				6BC5EE0124866D9500E1E78C /* Pager.swift in Sources */,
+				576BF5CC28E0CAAA00E73618 /* PagerData.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};

Example/SwiftUIPagerExample/Examples/InfiniteExampleView.swift

@@ -29,10 +29,10 @@ struct InfiniteExampleView: View {
                             self.pageView($0)
                     }
                     .singlePagination(ratio: 0.5, sensitivity: .high)
-                    .onPageWillChange({ (page) in
+                    .onPageWillChange({ (page, _) in
                         print("Page will change to: \(page)")
                     })
-                    .onPageChanged({ page in
+                    .onPageChanged({ page, _ in
                         print("Page changed to: \(page)")
                         if page == 1 {
                             let newData = (1...5).map { data1.first! - $0 }.reversed()

Sources/SwiftUIPager/PageWrapper.swift

@@ -21,8 +21,17 @@ struct PageWrapper<Element, ID>: Equatable, Identifiable where Element: Equatabl
     /// Wrappes Value
     var element: Element
 
+    var indexInData: Int
+
     /// `Identifiable` _id_
     var id: String {
         "\(batchId)-\(element[keyPath: keyPath])"
     }
+
+    init(batchId: UInt, keyPath: KeyPath<Element, ID>, element: Element, indexInData: Int = 0) {
+        self.batchId = batchId
+        self.keyPath = keyPath
+        self.element = element
+        self.indexInData = indexInData
+    }
 }

Sources/SwiftUIPager/Pager+Buildable.swift

@@ -330,7 +330,7 @@ extension Pager: Buildable {
     /// Adds a callback to react whenever the page changes
     ///
     /// - Parameter callback: block to be called when `page` changes
-    public func onPageChanged(_ callback: ((Int) -> Void)?) -> Self {
+    public func onPageChanged(_ callback: ((Int, Element) -> Void)?) -> Self {
         mutating(keyPath: \.onPageChanged, value: callback)
     }
 
@@ -345,7 +345,7 @@ extension Pager: Buildable {
     /// Adds a callback to react whenever the page will change
     ///
     /// - Parameter callback: block to be called when `page` will  change
-    public func onPageWillChange(_ callback: ((Int) -> Void)?) -> Self {
+    public func onPageWillChange(_ callback: ((Int, Element) -> Void)?) -> Self {
         mutating(keyPath: \.onPageWillChange, value: callback)
     }
 

Sources/SwiftUIPager/Pager.swift

@@ -59,7 +59,7 @@ public struct Pager<Element, ID, PageView>: View  where PageView: View, Element:
     let id: KeyPath<Element, ID>
 
     /// Array of items that will populate each page
-    var data: [Element]
+    var data: any PagerData<Element>
 
     /*** ViewModified properties ***/
 
@@ -148,13 +148,13 @@ public struct Pager<Element, ID, PageView>: View  where PageView: View, Element:
     var preferredItemSize: CGSize?
 
     /// Callback invoked when a new page will be set
-    var onPageWillChange: ((Int) -> Void)?
+    var onPageWillChange: ((Int, Element) -> Void)?
 
     /// Callback invoked when the user ends dragging and a transition will occur
     var onPageWillTransition: ((Result<PageTransition, PageTransitionError>) -> Void)?
 
     /// Callback invoked when a new page is set
-    var onPageChanged: ((Int) -> Void)?
+    var onPageChanged: ((Int, Element) -> Void)?
 
     /// Callback for a dragging began event
     var onDraggingBegan: (() -> Void)?
@@ -178,9 +178,9 @@ public struct Pager<Element, ID, PageView>: View  where PageView: View, Element:
     /// - Parameter data: Collection of items to populate the content
     /// - Parameter id: KeyPath to identifiable property
     /// - Parameter content: Factory method to build new pages
-    public init<Data: RandomAccessCollection>(page: Page, data: Data, id: KeyPath<Element, ID>, @ViewBuilder content: @escaping (Element) -> PageView) where Data.Index == Int, Data.Element == Element {
+    public init<Data: PagerData>(page: Page, data: Data, id: KeyPath<Element, ID>, @ViewBuilder content: @escaping (Element) -> PageView) where Data.Element == Element {
         self.pagerModel = page
-        self.data = Array(data)
+        self.data = data
         self.id = id
         self.content = content
         self.pagerModel.totalPages = data.count
@@ -261,8 +261,8 @@ extension Pager where ID == Element.ID, Element : Identifiable {
     /// - Parameter page: Current page index
     /// - Parameter data: Collection of items to populate the content
     /// - Parameter content: Factory method to build new pages
-    public init<Data: RandomAccessCollection>(page: Page, data: Data, @ViewBuilder content: @escaping (Element) -> PageView) where Data.Index == Int, Data.Element == Element {
-        self.init(page: page, data: Array(data), id: \Element.id, content: content)
+    public init<Data: PagerData>(page: Page, data: Data, @ViewBuilder content: @escaping (Element) -> PageView) where Data.Element == Element {
+        self.init(page: page, data: data, id: \Element.id, content: content)
     }
 
 }

Sources/SwiftUIPager/PagerContent+Buildable.swift

@@ -45,13 +45,7 @@ extension Pager.PagerContent: Buildable {
     /// pages on both the screen and the sides. If your sequence is not large enough, use `count` to
     /// repeat it and pass more elements.
     func loopPages(_ value: Bool = true, repeating count: UInt = 1) -> Self {
-        var newData = data
-        if let id = newData.first?.keyPath {
-            let count = max(1, count)
-            newData = (1...count).map { it in
-                data.map { PageWrapper(batchId: it, keyPath: id, element: $0.element) }
-            }.flatMap { $0 }
-        }
+        let newData = data.withRepeating(repeating: Int(count))
         self.pagerModel.isInfinite = value
         self.pagerModel.totalPages = newData.count
         return mutating(keyPath: \.isInifinitePager, value: value)
@@ -295,7 +289,7 @@ extension Pager.PagerContent: Buildable {
     /// Adds a callback to react whenever the page will change
     ///
     /// - Parameter callback: block to be called when `page` will  change
-    func onPageWillChange(_ callback: ((Int) -> Void)?) -> Self {
+    func onPageWillChange(_ callback: ((Int, Element) -> Void)?) -> Self {
         mutating(keyPath: \.onPageWillChange, value: callback)
     }
 
@@ -310,7 +304,7 @@ extension Pager.PagerContent: Buildable {
     /// Adds a callback to react whenever the page changes
     ///
     /// - Parameter callback: block to be called when `page` changes
-    func onPageChanged(_ callback: ((Int) -> Void)?) -> Self {
+    func onPageChanged(_ callback: ((Int, Element) -> Void)?) -> Self {
         mutating(keyPath: \.onPageChanged, value: callback)
     }
 

Sources/SwiftUIPager/PagerContent+Helper.swift

@@ -204,7 +204,7 @@ extension Pager.PagerContent {
 
     /// Extra offset to complentate the alignment
     var alignmentOffset: CGFloat {
-        let indexOfPageFocused = dataDisplayed.firstIndex(where: { data.firstIndex(of: $0) == self.page }) ?? 0
+        let indexOfPageFocused = dataDisplayed.firstIndex(where: { $0.indexInData == self.page }) ?? 0
 
         let offset: CGFloat
         switch (alignment, indexOfPageFocused) {
@@ -249,7 +249,7 @@ extension Pager.PagerContent {
 
     /// Offset applied to `HStack` along the X-Axis. It's limitted by `offsetLowerbound` and `offsetUpperbound`
     var xOffset: CGFloat {
-        let indexOfPageFocused = CGFloat(dataDisplayed.firstIndex(where: { data.firstIndex(of: $0) == self.page }) ?? 0)
+        let indexOfPageFocused = CGFloat(dataDisplayed.firstIndex(where: { $0.indexInData == self.page }) ?? 0)
         let numberOfPages = CGFloat(numberOfPagesDisplayed)
         let xIncrement = pageDistance / 2
         let offset = (numberOfPages / 2 - indexOfPageFocused) * pageDistance - xIncrement + totalOffset + alignmentOffset

Sources/SwiftUIPager/PagerContent.swift

@@ -43,7 +43,7 @@ extension Pager {
         let id: KeyPath<PageWrapper<Element, ID>, String>
 
         /// Array of items that will populate each page
-        var data: [PageWrapper<Element, ID>]
+        var data: PagerWrapperData<Element, ID>
 
         /*** ViewModified properties ***/
 
@@ -126,13 +126,13 @@ extension Pager {
         var preferredItemSize: CGSize?
 
         /// Callback invoked when a new page will be set
-        var onPageWillChange: ((Int) -> Void)?
+        var onPageWillChange: ((Int, Element) -> Void)?
 
         /// Callback invoked when the user ends dragging and a transition will occur
         var onPageWillTransition: ((Result<PageTransition, PageTransitionError>) -> Void)?
 
         /// Callback invoked when a new page is set
-        var onPageChanged: ((Int) -> Void)?
+        var onPageChanged: ((Int, Element) -> Void)?
 
         /// Callback for a dragging began event
         var onDraggingBegan: (() -> Void)?
@@ -170,10 +170,10 @@ extension Pager {
         /// - Parameter data: Array of items to populate the content
         /// - Parameter id: KeyPath to identifiable property
         /// - Parameter content: Factory method to build new pages
-        init(size: CGSize, pagerModel: Page, data: [Element], id: KeyPath<Element, ID>, @ViewBuilder content: @escaping (Element) -> PageView) {
+        init(size: CGSize, pagerModel: Page, data: some PagerData<Element>, id: KeyPath<Element, ID>, @ViewBuilder content: @escaping (Element) -> PageView) {
             self.size = size
             self.pagerModel = pagerModel
-            self.data = data.map { PageWrapper(batchId: 1, keyPath: id, element: $0) }
+            self.data = PagerWrapperData(wrapper: data, id: id)
             self.id = \PageWrapper<Element, ID>.id
             self.content = content
         }
@@ -229,7 +229,7 @@ extension Pager {
 
                         if pagerModel.pageIncrement != 0 {
                             pagerModel.pageIncrement = 0
-                            onPageChanged?(pagerModel.index)
+                            onPageChanged?(pagerModel.index, data.itemFor(index: pagerModel.index).element)
                         }
                     })
                     .eraseToAny()
@@ -388,7 +388,7 @@ extension Pager.PagerContent {
 
         let animation = pagingAnimation.animation?.speed(speed)
         if page != newPage {
-            onPageWillChange?(newPage)
+            onPageWillChange?(newPage, data.itemFor(index: newPage).element)
             onPageWillTransition?(.success(.init(currentPage: page, nextPage: newPage, pageIncrement: pageIncrement)))
         } else {
             onPageWillTransition?(.failure(.draggingStopped))
@@ -411,7 +411,7 @@ extension Pager.PagerContent {
             // Do nothing
         } else if page != newPage {
             self.pagerModel.pageIncrement = 0
-            onPageChanged?(newPage)
+            onPageChanged?(newPage, data.itemFor(index: newPage).element)
         }
     }
 

Sources/SwiftUIPager/PagerData.swift

@@ -0,0 +1,56 @@
+//
+//  File.swift
+//  
+//
+//  Created by feichao on 2022/9/25.
+//
+
+import Foundation
+
+public protocol PagerData<Element> {
+    associatedtype Element
+
+    func itemFor(index: Int) -> Element
+
+    var count: Int { get }
+}
+
+
+struct PagerWrapperData<Element, ID> where Element: Equatable, ID: Hashable {
+    let wrapper: any PagerData<Element>
+    let id: KeyPath<Element, ID>
+    var repeating: Int
+
+    init<T: PagerData<Element>>(wrapper: T, id: KeyPath<Element, ID>, repeating: Int = 1) {
+        self.wrapper = wrapper
+        self.id = id
+        self.repeating = repeating
+    }
+
+    func itemFor(index: Int) -> PageWrapper<Element, ID> {
+        assert(index < count * repeating)
+        let batch = index / count
+        let item = wrapper.itemFor(index: index % count)
+        return PageWrapper(batchId: UInt(batch), keyPath: id, element: item, indexInData: index)
+    }
+
+    var count: Int {
+        wrapper.count * repeating
+    }
+
+    subscript(index: Int) -> PageWrapper<Element, ID> {
+        return itemFor(index: index)
+    }
+
+    func withRepeating(repeating: Int) -> Self {
+        var new = self
+        new.repeating = repeating
+        return new
+    }
+}
+
+extension Array: PagerData {
+    public func itemFor(index: Int) -> Element {
+        self[index]
+    }
+}

Tests/SwiftUIPagerTests/Pager+Buildable_Tests.swift

@@ -519,7 +519,7 @@ final class Pager_Buildable_Tests: XCTestCase {
     }
 
     func test_GivenPager_WhenOnPageChanged_ThenCallbackNotNil() {
-        let pager = givenPager.onPageChanged { _ in }
+        let pager = givenPager.onPageChanged { _, _ in }
         let pagerContent = pager.content(for: CGSize(width: 100, height: 100))
         XCTAssertNotNil(pagerContent.onPageChanged)
     }
@@ -563,7 +563,7 @@ final class Pager_Buildable_Tests: XCTestCase {
         var pager = givenPager
 
         var newPage: Int? = nil
-        pager = pager.onPageWillChange({ (page) in
+        pager = pager.onPageWillChange({ (page, _) in
             newPage = page
         })
 
@@ -579,7 +579,7 @@ final class Pager_Buildable_Tests: XCTestCase {
         var pager = givenPager
 
         var newPage: Int? = nil
-        pager = pager.onPageWillChange({ (page) in
+        pager = pager.onPageWillChange({ (page, _) in
             newPage = page
         })