optimize SwiftUI.View+SizeThatFits

Author: honghaoz

ComposeUI/Sources/ComposeUI/SwiftUI/SwiftUI.View+SizeThatFits.swift

@@ -46,11 +46,41 @@ public extension SwiftUI.View {
   ///   - proposingSize: The proposing container size.
   /// - Returns: The fitting size of the view.
   func sizeThatFits(_ proposingSize: CGSize) -> CGSize {
-    #if canImport(AppKit)
-    return NSHostingController(rootView: self).sizeThatFits(in: proposingSize)
-    #endif
-    #if canImport(UIKit)
-    return UIHostingController(rootView: self).sizeThatFits(in: proposingSize)
-    #endif
+    SwiftUISizingHostPool.shared.sizeThatFits(self, in: proposingSize)
+  }
+}
+
+#if canImport(AppKit)
+private typealias HostingController = NSHostingController
+#endif
+
+#if canImport(UIKit)
+private typealias HostingController = UIHostingController
+#endif
+
+/// A pool of `HostingController` instances used to measure SwiftUI views, to avoid per-call `HostingController` allocation cost.
+///
+/// A pool (rather than a single shared host) is used so that reentrant calls, e.g. a parent view's body calls `sizeThatFits` on a child
+/// while the parent itself is being measured, each get their own dedicated host controller.
+///
+/// The pool grows lazily to match the deepest observed reentrancy and stays at that size afterwards.
+@MainActor
+private final class SwiftUISizingHostPool {
+
+  static let shared = SwiftUISizingHostPool()
+
+  private var hosts: [HostingController<AnyView>] = []
+
+  private init() {}
+
+  func sizeThatFits(_ view: some SwiftUI.View, in proposingSize: CGSize) -> CGSize {
+    let host = hosts.popLast() ?? HostingController(rootView: AnyView(EmptyView()))
+    host.rootView = AnyView(view)
+    defer {
+      // drop the reference to the user's view before returning the host to the pool.
+      host.rootView = AnyView(EmptyView())
+      hosts.append(host)
+    }
+    return host.sizeThatFits(in: proposingSize)
   }
 }

ComposeUI/Tests/ComposeUITests/CrossPlatform/UniversalTypesTests.swift

@@ -0,0 +1,118 @@
+//
+//  UniversalTypesTests.swift
+//  ComposéUI
+//
+//  Created by Honghao Zhang on 5/9/26.
+//  Copyright © 2024 Honghao Zhang.
+//
+//  MIT License
+//
+//  Copyright (c) 2024 Honghao Zhang (github.com/honghaoz)
+//
+//  Permission is hereby granted, free of charge, to any person obtaining a copy
+//  of this software and associated documentation files (the "Software"), to
+//  deal in the Software without restriction, including without limitation the
+//  rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+//  sell copies of the Software, and to permit persons to whom the Software is
+//  furnished to do so, subject to the following conditions:
+//
+//  The above copyright notice and this permission notice shall be included in
+//  all copies or substantial portions of the Software.
+//
+//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+//  FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+//  IN THE SOFTWARE.
+//
+
+#if canImport(AppKit)
+import AppKit
+#endif
+
+#if canImport(UIKit)
+import UIKit
+#endif
+
+import ChouTiTest
+
+import ComposeUI
+
+final class UniversalTypesTests: XCTestCase {
+
+  // MARK: - AppKit
+
+  #if canImport(AppKit)
+
+  func test_appKit_typealiases() {
+    expect(ComposeUI.Window.self == NSWindow.self) == true
+    expect(ComposeUI.View.self == NSView.self) == true
+    expect(ComposeUI.TextView.self == NSTextView.self) == true
+    expect(ComposeUI.Color.self == NSColor.self) == true
+    expect(ComposeUI.Font.self == NSFont.self) == true
+    expect(ComposeUI.FontDescriptor.self == NSFontDescriptor.self) == true
+    expect(ComposeUI.BezierPath.self == NSBezierPath.self) == true
+    expect(ComposeUI.GestureRecognizer.self == NSGestureRecognizer.self) == true
+    expect(ComposeUI.TapGestureRecognizer.self == NSClickGestureRecognizer.self) == true
+    expect(ComposeUI.PressGestureRecognizer.self == NSPressGestureRecognizer.self) == true
+    expect(ComposeUI.PanGestureRecognizer.self == NSPanGestureRecognizer.self) == true
+  }
+
+  func test_appKit_edgeInsets_isNSEdgeInsets() {
+    let insets = ComposeUI.EdgeInsets(top: 1, left: 2, bottom: 3, right: 4)
+    expect(insets.top) == 1
+    expect(insets.left) == 2
+    expect(insets.bottom) == 3
+    expect(insets.right) == 4
+    // confirm interop with NSEdgeInsets
+    let nsInsets: NSEdgeInsets = insets
+    expect(nsInsets.top) == 1
+  }
+
+  func test_appKit_gestureRecognizerDelegate_protocolConformance() {
+    final class Delegate: NSObject, ComposeUI.GestureRecognizerDelegate {}
+    let delegate: NSGestureRecognizerDelegate = Delegate()
+    expect(delegate).toNot(beNil())
+  }
+
+  #endif
+
+  // MARK: - UIKit
+
+  #if canImport(UIKit)
+
+  func test_uiKit_typealiases() {
+    expect(ComposeUI.Window.self == UIWindow.self) == true
+    expect(ComposeUI.View.self == UIView.self) == true
+    expect(ComposeUI.TextView.self == UITextView.self) == true
+    expect(ComposeUI.Color.self == UIColor.self) == true
+    expect(ComposeUI.Font.self == UIFont.self) == true
+    expect(ComposeUI.FontDescriptor.self == UIFontDescriptor.self) == true
+    expect(ComposeUI.BezierPath.self == UIBezierPath.self) == true
+    expect(ComposeUI.GestureRecognizer.self == UIGestureRecognizer.self) == true
+    expect(ComposeUI.TapGestureRecognizer.self == UITapGestureRecognizer.self) == true
+    expect(ComposeUI.PressGestureRecognizer.self == UILongPressGestureRecognizer.self) == true
+    expect(ComposeUI.PanGestureRecognizer.self == UIPanGestureRecognizer.self) == true
+  }
+
+  func test_uiKit_edgeInsets_isUIEdgeInsets() {
+    let insets = ComposeUI.EdgeInsets(top: 1, left: 2, bottom: 3, right: 4)
+    expect(insets.top) == 1
+    expect(insets.left) == 2
+    expect(insets.bottom) == 3
+    expect(insets.right) == 4
+    // confirm interop with UIEdgeInsets
+    let uiInsets: UIEdgeInsets = insets
+    expect(uiInsets.top) == 1
+  }
+
+  func test_uiKit_gestureRecognizerDelegate_protocolConformance() {
+    final class Delegate: NSObject, ComposeUI.GestureRecognizerDelegate {}
+    let delegate: UIGestureRecognizerDelegate = Delegate()
+    expect(delegate).toNot(beNil())
+  }
+
+  #endif
+}