SwiftUI：解决.fullScreenCover转屏动画时背景色失效问题

使用SwiftUI的.fullScreenCover()视图修饰器并设置背景后，该背景在屏幕方向切换动画过程中无法生效。

如何消除转屏动画期间的白色背景？

示例代码：

import SwiftUI

struct ContentView: View {
    var body: some View {
        VStack {
            Spacer()
            HStack {
                Spacer()
            }
        }
        .fullScreenCover(isPresented: .constant(true)) {
            VStack {
                Spacer()
                HStack {
                    Spacer()
                }
            }
            .background(Color.black.ignoresSafeArea())
        }
        .background(Color.red.ignoresSafeArea())
    }
}

转屏时的问题表现：视图调整尺寸过程中会（部分）显示白色背景（动画效果如下）：

这个问题源于fullScreenCover的容器在转屏动画期间未被正确填充背景色，可通过以下几种方式解决：

方法一：为全屏覆盖视图绑定窗口级背景 #

通过设置应用窗口背景，确保转屏动画期间无空白区域：

import SwiftUI

struct ContentView: View {
    var body: some View {
        VStack {
            Spacer()
            HStack {
                Spacer()
            }
        }
        .fullScreenCover(isPresented: .constant(true)) {
            FullScreenContentView()
        }
        .background(Color.red.ignoresSafeArea())
    }
}

struct FullScreenContentView: View {
    var body: some View {
        ZStack {
            Color.black
                .ignoresSafeArea(.all)
                .onAppear {
                    // 设置窗口背景
                    if let window = UIApplication.shared.windows.first {
                        window.backgroundColor = .black
                    }
                }
                .onDisappear {
                    // 恢复默认窗口背景
                    if let window = UIApplication.shared.windows.first {
                        window.backgroundColor = .systemBackground
                    }
                }
            
            // 原有内容布局
            VStack {
                Spacer()
                HStack {
                    Spacer()
                }
            }
        }
    }
}

方法二：自定义UIKit全屏覆盖控制器 #

通过UIKit的UIViewController实现全屏覆盖，规避SwiftUI层级限制：

import SwiftUI

struct CustomFullScreenCover<Content: View>: UIViewControllerRepresentable {
    @Binding var isPresented: Bool
    let content: () -> Content
    
    func makeUIViewController(context: Context) -> UIViewController {
        UIViewController()
    }
    
    func updateUIViewController(_ uiViewController: UIViewController, context: Context) {
        if isPresented {
            let hostingController = UIHostingController(rootView: content())
            hostingController.view.backgroundColor = .black
            hostingController.modalPresentationStyle = .fullScreen
            uiViewController.present(hostingController, animated: true)
        } else {
            uiViewController.dismiss(animated: true)
        }
    }
}

// 使用示例
struct ContentView: View {
    @State private var showCover = true
    
    var body: some View {
        VStack {
            Spacer()
            HStack {
                Spacer()
            }
        }
        .background(Color.red.ignoresSafeArea())
        .customFullScreenCover(isPresented: $showCover) {
            VStack {
                Spacer()
                HStack {
                    Spacer()
                }
            }
            .background(Color.black.ignoresSafeArea())
        }
    }
}

方法三：使用presentationBackground修饰器（iOS 16+） #

若项目支持iOS 16及以上版本，可直接用原生修饰器解决：

import SwiftUI

struct ContentView: View {
    var body: some View {
        VStack {
            Spacer()
            HStack {
                Spacer()
            }
        }
        .fullScreenCover(isPresented: .constant(true)) {
            VStack {
                Spacer()
                HStack {
                    Spacer()
                }
            }
        }
        .presentationBackground(Color.black.ignoresSafeArea()) // 关键代码
        .background(Color.red.ignoresSafeArea())
    }
}

内容的提问来源于stack exchange，提问作者NicolasBrunner