Fix repeated evaluation on scroll

CHANGELOG.md

@@ -1,6 +1,26 @@
 # Change Log
 All notable changes to this project will be documented in this file.
 
+## 3.0.0
+
+### Breaking Changes
+
+* Minimum deployment target raised to iOS 18. iOS 17 is no longer supported.
+* `HeaderContext` converted from a struct to an `@Observable` class to address performance issues related to SwiftData queries. The observable class shields content views from re-performing queries and re-evaluating `body` on every frame while scrolling. If you stored `HeaderContext` (or its typealiases `MaterialTabsHeaderContext` / `StickyHeaderContext`) by value, you will need to update to reference semantics.
+* #19 `MaterialTabsScroll` joint scroll position API replaced with iOS 18 `ScrollPosition`. The old `scrollAnchor` parameter is replaced by optional `scrollPosition` and `anchor` bindings for joint scroll position manipulation between the library and client code.
+
+### Improvements
+
+* #25 `MaterialTabBar` now supports an `alignment` parameter (`.leading`, `.center`, `.trailing`) for controlling horizontal positioning of self-sized tabs when `fillAvailableSpace` is `false`.
+* #25 New `MaterialAccessoryTabBar` component for adding optional leading and trailing accessory views alongside tab selectors. Accessories scroll horizontally with the tabs.
+* #25 `TabBarModel` and `HeaderModel` are now public, enabling fully custom tab bar implementations via the environment.
+
+## 2.0.7
+
+### Improvements
+
+* Add context-free initializers to `MaterialTabsScroll` and `StickyHeaderScroll`. The existing initializers pass a `MaterialTabsScrollContext` (or `StickyHeaderScrollContext`) to the content view builder, which includes the content offset. Because the content offset changes on every frame during scrolling, this causes the content view `body` to be re-evaluated continuously. The new initializers omit the context, allowing the content to be shielded from these unnecessary re-evaluations via an internal `ContentWrapperView` with `Equatable` conformance. If your content does not need the context, prefer the new initializers for better scroll performance.
+
 ## 2.0.6
 
 ### Fixes

Demo/Demo/Preview Content/TestMaterialTabsScroll.swift

@@ -18,8 +18,8 @@ struct TestMaterialTabsScroll: View {
     // MARK: - Variables
 
     @State private var selectedTab = 0
-    @State private var scrollItem: Int?
-    @State private var scrollUnitPoint: UnitPoint = .top
+    @State private var scrollPosition = ScrollPosition(idType: Int.self)
+    @State private var scrollAnchor: UnitPoint? = .top
 
     // MARK: - Body
 
@@ -30,28 +30,52 @@ struct TestMaterialTabsScroll: View {
                 Text("Title").frame(height: titleHeight)
             },
             headerTabBar: { context in
-                Text("Tab Bar").frame(height: tabBarHeight)
+                HStack(spacing: 0) {
+                    ForEach(0..<2) { tab in
+                        Button {
+                            selectedTab = tab
+                        } label: {
+                            Text("Tab \(tab)")
+                                .frame(maxWidth: .infinity)
+                                .padding(.vertical, 12)
+                                .background(selectedTab == tab ? Color.blue.opacity(0.2) : Color.clear)
+                        }
+                    }
+                }
+                .frame(height: tabBarHeight)
             },
             headerBackground: { _ in
                 Color.yellow.opacity(0.25)
             }
         ) {
             MaterialTabsScroll(
                 tab: 0,
-                reservedItem: -1,
-                scrollItem: $scrollItem,
-                scrollUnitPoint: $scrollUnitPoint
+                scrollPosition: $scrollPosition,
+                anchor: $scrollAnchor
             ) { _ in
                 LazyVStack(spacing: 0) {
                     ForEach(0..<25) { index in
                         VStack(spacing: 0) {
                             Rectangle().fill(.black.opacity(0.2)).frame(height: 1)
                             Spacer()
-                            Button("Tap Row \(index)") {
-                                scrollUnitPoint = .top
-                                scrollItem = index
+                            HStack {
+                                Text("Row \(index)")
+                                Spacer()
+                                Button("Top") {
+                                    withAnimation {
+                                        scrollAnchor = .top
+                                        scrollPosition.scrollTo(id: index, anchor: .top)
+                                    }
+                                }
+                                Button("Bottom") {
+                                    withAnimation {
+                                        scrollAnchor = .bottom
+                                        scrollPosition.scrollTo(id: index, anchor: .bottom)
+                                    }
+                                }
                             }
                             .buttonStyle(.bordered)
+                            .padding(.horizontal)
                             Spacer()
                         }
                         .frame(height: rowHeight)
@@ -60,8 +84,22 @@ struct TestMaterialTabsScroll: View {
                 }
                 .scrollTargetLayout()
             }
+            .materialTabItem(tab: 0, label: .secondary("Tab 0"))
+            MaterialTabsScroll(tab: 1) { _ in
+                LazyVStack(spacing: 0) {
+                    ForEach(0..<25) { index in
+                        VStack(spacing: 0) {
+                            Rectangle().fill(.black.opacity(0.2)).frame(height: 1)
+                            Spacer()
+                            Text("Tab 1 — Row \(index)")
+                            Spacer()
+                        }
+                        .frame(height: rowHeight)
+                    }
+                }
+            }
+            .materialTabItem(tab: 1, label: .secondary("Tab 1"))
         }
-        .animation(.default, value: scrollItem)
     }
 }
 

Package.swift

@@ -1,11 +1,11 @@
-// swift-tools-version: 5.9
+// swift-tools-version: 6.0
 // The swift-tools-version declares the minimum version of Swift required to build this package.
 
 import PackageDescription
 
 let package = Package(
     name: "SwiftUIMaterialTabs",
-    platforms: [.iOS(.v17)],
+    platforms: [.iOS(.v18)],
     products: [
         // Products define the executables and libraries a package produces, making them visible to other packages.
         .library(