A forked version of ContainerRelativeFrame

myContainerRelativeFrame.swift

import Combine
import Foundation
import SwiftUI
import UIKit

extension UIView {
  fileprivate func findRelevantContainer() -> ContainerType? {
    var responder: UIResponder? = self

    while let currentResponder = responder {
      if let viewController = currentResponder as? UIViewController {
        if let tabview = viewController as? UITabBarController {
          return .tabview(tabview) // UITabBarController
        }
        if let navigator = viewController as? UINavigationController {
          return .navigator(navigator) // UINavigationController
        }
      }
      if let scrollView = currentResponder as? UIScrollView {
        return .scrollView(scrollView) // UIScrollView
      }
      responder = currentResponder.next
    }

    if let currentWindow {
      return .window(currentWindow) // UIWindow
    } else {
      return nil
    }
  }
}

private struct ContainerDetector: UIViewRepresentable {
  @Binding var size: CGSize?
  func makeCoordinator() -> Coordinator {
    .init(size: _size)
  }

  init(size: Binding<CGSize?>) {
    _size = size
  }

  func makeUIView(context _: Context) -> UIView {
    let detector = UIView()
    detector.backgroundColor = .clear
    return detector
  }

  func updateUIView(_ uiview: UIView, context: Context) {
    DispatchQueue.main.async {
      guard context.coordinator.cancellable == nil else { return }
      if let container = uiview.findRelevantContainer() {
        context.coordinator.trackContainerSizeChanges(ofType: container)
      }
    }
  }

  @MainActor
  class Coordinator: NSObject, ObservableObject {
    var size: Binding<CGSize?>
    var cancellable: AnyCancellable?

    init(size: Binding<CGSize?>) {
      self.size = size
    }

    func trackContainerSizeChanges(ofType type: ContainerType) {
      switch type {
      case let .window(window):
        cancellable = window.publisher(for: \.frame)
          .receive(on: RunLoop.main)
          .sink(receiveValue: { [weak self] _ in
            guard let self = self else { return }
            let size = self.calculateContainerSize(ofType: type)
            self.size.wrappedValue = size
          })

      case let .navigator(navigator):
        cancellable = navigator.view.publisher(for: \.frame)
          .receive(on: RunLoop.main)
          .sink { [weak self] _ in
            guard let self = self else { return }
            let size = self.calculateContainerSize(ofType: type)
            self.size.wrappedValue = size
          }

      case let .scrollView(scrollView): // scrollView is UIScrollView
        cancellable = scrollView.publisher(for: \.frame)
          .receive(on: RunLoop.main)
          .sink { [weak self] _ in
            guard let self = self else { return }
            let size = self.calculateContainerSize(ofType: type)
            self.size.wrappedValue = size
          }

      case let .tabview(tabview):
        cancellable = tabview.view.publisher(for: \.frame)
          .receive(on: RunLoop.main)
          .sink { [weak self] _ in
            guard let self = self else { return }
            let size = self.calculateContainerSize(ofType: type)
            self.size.wrappedValue = size
          }
      }
    }

    func calculateContainerSize(ofType type: ContainerType) -> CGSize {
      switch type {
      case let .window(window):
        let windowSize = window.frame.size
        let safeAreaInsets = window.safeAreaInsets
        let width = windowSize.width - safeAreaInsets.left - safeAreaInsets.right
        let height = windowSize.height - safeAreaInsets.top - safeAreaInsets.bottom
        return CGSize(width: width, height: height)

      case let .navigator(navigator):

        let navigatorSize = navigator.view.frame.size
        let safeAreaInsets = navigator.view.safeAreaInsets
        var navigationBarHeight: CGFloat = 0
        // 在 NavigationSplitView 中时，计算高度需要去除 barHeight
        if navigator.parent is UISplitViewController {
          navigationBarHeight = navigator.navigationBar.frame.height
        }
        let width = navigatorSize.width - safeAreaInsets.left - safeAreaInsets.right
        let height = navigatorSize.height - safeAreaInsets.top - safeAreaInsets.bottom - navigationBarHeight
        return CGSize(width: width, height: height)

      case let .scrollView(scrollview):

        let scrollviewSize = scrollview.frame.size
        let safeAreaInsets = scrollview.safeAreaInsets
        let width = scrollviewSize.width - safeAreaInsets.left - safeAreaInsets.right
        let height = scrollviewSize.height - safeAreaInsets.top - safeAreaInsets.bottom
        return CGSize(width: width, height: height)

      case let .tabview(tabview):

        let tabviewSize = tabview.view.frame.size
        let barHeight = tabview.tabBar.frame.height
        let safeAreaInsets = tabview.view.safeAreaInsets
        let width = tabviewSize.width - safeAreaInsets.left - safeAreaInsets.right
        // tabview 底部高度要去除 barHeight
        let height = tabviewSize.height - safeAreaInsets.top - barHeight
        return CGSize(width: width, height: height)
      }
    }
  }
}

private enum ContainerType {
  case scrollView(UIScrollView)
  case navigator(UINavigationController)
  case tabview(UITabBarController)
  case window(UIWindow)
}

extension UIView {
  // UIView 对应的 UIWindow
  fileprivate var currentWindow: UIWindow? {
    var parentResponder: UIResponder? = self
    while let nextResponder = parentResponder?.next {
      parentResponder = nextResponder
      if let window = parentResponder as? UIWindow {
        return window
      }
    }
    return nil
  }
}

private struct ContainerDetectorModifier: ViewModifier {
  let type: DetectorType
  @State private var containerSize: CGSize?
  func body(content: Content) -> some View {
    let sizeInfo = result
    content
      .background(
        ContainerDetector(size: $containerSize)
      )
      .frame(width: sizeInfo.width, height: sizeInfo.height, alignment: sizeInfo.alignment)
  }

  var result: (width: CGFloat?, height: CGFloat?, alignment: Alignment) {
    var width: CGFloat?
    var height: CGFloat?
    var align: Alignment = .center
    switch type {
    case let .standard(axes, alignment):
      if axes.contains(.horizontal) {
        width = containerSize?.width
      }
      if axes.contains(.vertical) {
        height = containerSize?.height
      }
      align = alignment

    case let .custom(axes, alignment, length):
      if axes.contains(.horizontal), let w = containerSize?.width {
        width = length(w, .horizontal)
      }
      if axes.contains(.vertical), let h = containerSize?.height {
        height = length(h, .vertical)
      }
      align = alignment

    case let .grid(axes, count, span, spacing, alignment):
      if axes.contains(.horizontal), let w = containerSize?.width {
        let availableWidth = (w - (spacing * CGFloat(count - 1)))
        let columnWidth = (availableWidth / CGFloat(count))
        width = (columnWidth * CGFloat(span)) + (CGFloat(span - 1) * spacing)
      }
      if axes.contains(.vertical), let h = containerSize?.height {
        let availableHeight = (h - (spacing * CGFloat(count - 1)))
        let rowHeight = (availableHeight / CGFloat(count))
        height = (rowHeight * CGFloat(span)) + (CGFloat(span - 1) * spacing)
      }
      align = alignment
    }
    if width ?? 0 < 0 { width = nil }
    if height ?? 0 < 0 { width = nil }
    return (width, height, align)
  }

  enum DetectorType {
    case standard(axes: Axis.Set, alignment: Alignment)
    case grid(axes: Axis.Set, count: Int, span: Int, spacing: CGFloat, alignment: Alignment)
    case custom(axes: Axis.Set, alignment: Alignment, length: (CGFloat, Axis) -> CGFloat)
  }
}

extension View {
  @available(iOS 13.0, *)
  public func myContainerRelativeFrame(_ axes: Axis.Set, alignment: Alignment = .center) -> some View {
    modifier(ContainerDetectorModifier(type: .standard(axes: axes, alignment: alignment)))
  }

  @available(iOS 13.0,*)
  public func myContainerRelativeFrame(_ axes: Axis.Set, count: Int, span: Int = 1, spacing: CGFloat, alignment: Alignment = .center) -> some View {
    modifier(ContainerDetectorModifier(type: .grid(axes: axes, count: count, span: span, spacing: spacing, alignment: alignment)))
  }

  @available(iOS 13.0,*)
  public func myContainerRelativeFrame(_ axes: Axis.Set, alignment: Alignment = .center, _ length: @escaping (CGFloat, Axis) -> CGFloat) -> some View {
    modifier(ContainerDetectorModifier(type: .custom(axes: axes, alignment: alignment, length: length)))
  }
}

1. ContainerType 可以加上关联值，使用 container 时不用做类型转换；
2. .frame(width: result.width, height: result.height, alignment: result.alignment) 这里感觉会计算 3 次 result，用 @State 保存会好一点？

感谢指正。代码写的比较匆忙，主要为了对猜想做验证。代码已经做了调整