iOS16弹出模态视图时GeometryReader异常：Bug还是新特性？

问题概述 #

升级iOS 16后，SwiftUI中的GeometryReader出现异常：按特定操作步骤后，它返回的全局frame值会停留在模态视图弹出时的3D效果对应尺寸，无法自动恢复，导致依赖该值的视图变形。iOS 15中无此问题，已提交Bug报告。

环境信息 #

• Xcode 14
• iOS 15.5和16的模拟器/真机

复现步骤 #

1. 打开模态视图
2. 将应用切换至后台
3. 重新打开应用
4. 关闭模态视图

最小复现代码 #

struct ContentView: View {
    @State private var isPresented: Bool = false

    var body: some View {
        GeometryReader { reader in
            VStack(spacing: 36) {
                Text("Screen frame:\n\(String(describing: reader.frame(in: .global)))")
                    .multilineTextAlignment(.center)

                Button {
                    isPresented.toggle()
                } label: {
                    Text("Open modal")
                }
            }
            .frame(maxWidth: .infinity, maxHeight: .infinity)
            .padding()
            .onReceive(NotificationCenter.default.appDidBecomeActive()) { _ in
                print(reader.frame(in: .global))
            }
            .onReceive(NotificationCenter.default.appDidEnterBackground()) { _ in
                print(reader.frame(in: .global))
            }
        }
        .sheet(isPresented: $isPresented) {
            modalView
        }
    }

    private var modalView: some View {
        VStack {
            Image(systemName: "globe")
                .imageScale(.large)
                .foregroundColor(.accentColor)
            Text("Hello, world!")
        }
        .padding()
    }
}

extension NotificationCenter {
    func appDidBecomeActive() -> AnyPublisher<Notification, Never> {
        publisher(for: UIApplication.didBecomeActiveNotification).eraseToAnyPublisher()
    }

    func appDidEnterBackground() -> AnyPublisher<Notification, Never> {
        publisher(for: UIApplication.didEnterBackgroundNotification).eraseToAnyPublisher()
    }
}

强制GeometryReader重新计算的可行方案 #

方案1：用状态变量触发视图重建 #

新增一个状态变量，在模态关闭、应用激活等关键时机更新它，通过绑定id让GeometryReader所在视图重新构建，从而触发frame重新计算：

struct ContentView: View {
    @State private var isPresented: Bool = false
    @State private var refreshTrigger = 0 // 用于触发刷新的状态变量

    var body: some View {
        GeometryReader { reader in
            VStack(spacing: 36) {
                Text("Screen frame:\n\(String(describing: reader.frame(in: .global)))")
                    .multilineTextAlignment(.center)

                Button {
                    isPresented.toggle()
                } label: {
                    Text("Open modal")
                }
            }
            .frame(maxWidth: .infinity, maxHeight: .infinity)
            .padding()
            .onReceive(NotificationCenter.default.appDidBecomeActive()) { _ in
                print(reader.frame(in: .global))
            }
            .onReceive(NotificationCenter.default.appDidEnterBackground()) { _ in
                print(reader.frame(in: .global))
            }
        }
        .sheet(isPresented: $isPresented) {
            modalView
                .onDisappear {
                    // 模态关闭时触发刷新
                    refreshTrigger += 1
                }
        }
        .onReceive(NotificationCenter.default.appDidBecomeActive()) { _ in
            // 应用激活时也触发刷新
            refreshTrigger += 1
        }
        .id(refreshTrigger) // 值变化时，视图会完全重建
    }

    private var modalView: some View {
        VStack {
            Image(systemName: "globe")
                .imageScale(.large)
                .foregroundColor(.accentColor)
            Text("Hello, world!")
        }
        .padding()
    }
}

方案2：用UUID作为视图标识触发刷新 #

和方案1逻辑类似，改用UUID作为唯一标识，每次需要刷新时生成新的UUID，确保视图完全重建：

struct ContentView: View {
    @State private var isPresented: Bool = false
    @State private var viewID = UUID()

    var body: some View {
        GeometryReader { reader in
            VStack(spacing: 36) {
                Text("Screen frame:\n\(String(describing: reader.frame(in: .global)))")
                    .multilineTextAlignment(.center)

                Button {
                    isPresented.toggle()
                } label: {
                    Text("Open modal")
                }
            }
            .frame(maxWidth: .infinity, maxHeight: .infinity)
            .padding()
            .onReceive(NotificationCenter.default.appDidBecomeActive()) { _ in
                print(reader.frame(in: .global))
            }
            .onReceive(NotificationCenter.default.appDidEnterBackground()) { _ in
                print(reader.frame(in: .global))
            }
        }
        .sheet(isPresented: $isPresented) {
            modalView
                .onDisappear {
                    refreshView()
                }
        }
        .onReceive(NotificationCenter.default.appDidBecomeActive()) { _ in
            refreshView()
        }
        .id(viewID)
    }

    private func refreshView() {
        viewID = UUID()
    }

    private var modalView: some View {
        VStack {
            Image(systemName: "globe")
                .imageScale(.large)
                .foregroundColor(.accentColor)
            Text("Hello, world!")
        }
        .padding()
    }
}

方案3：替换全局frame获取方式（如果场景允许） #

如果你的视图不需要依赖GeometryReader的动态布局，直接用UIScreen.main.bounds获取屏幕尺寸，避开GeometryReader的异常：

// 替换原有Text中的frame获取逻辑
Text("Screen frame:\n\(String(describing: UIScreen.main.bounds))")

内容的提问来源于stack exchange，提问作者bguidolim