// 定义环境键
private struct CustomThemeKey: EnvironmentKey {
    static let defaultValue: Color = .blue // 默认颜色为蓝色
}

extension EnvironmentValues {
    var customTheme: Color {
        get { self[CustomThemeKey.self] }
        set { self[CustomThemeKey.self] = newValue }
    }
}

struct ChildView: View {
    @Environment(\.customTheme) private var themeColor // 读取环境变量
    
    var body: some View {
        Text("子视图")
            .foregroundStyle(themeColor) // 应用环境变量
    }
}

struct ParentView: View {
    var body: some View {
        ChildView()
            .environment(\.customTheme, .red) // 覆盖默认值为红色
    }
}

import SwiftUI

// 步骤1：定义环境键
private struct CustomThemeKey: EnvironmentKey {
    static let defaultValue: Color = .blue
}

// 步骤2：扩展 EnvironmentValues
extension EnvironmentValues {
    var customTheme: Color {
        get { self[CustomThemeKey.self] }
        set { self[CustomThemeKey.self] = newValue }
    }
}

// 步骤3：子视图读取环境变量
struct ChildView: View {
    @Environment(\.customTheme) private var themeColor
    
    var body: some View {
        VStack {
            Text("当前主题颜色")
                .font(.title)
                .foregroundStyle(themeColor)
            
            Divider()
            
            GrandchildView()
        }
    }
}

// 孙视图（继承父视图的环境变量）
struct GrandchildView: View {
    @Environment(\.customTheme) private var themeColor
    
    var body: some View {
        Button("按钮") {}
            .padding()
            .background(themeColor)
            .foregroundStyle(.white)
            .cornerRadius(10)
    }
}

// 步骤4：父视图设置环境变量
struct ParentView: View {
    var body: some View {
        VStack {
            // 默认环境变量（蓝色）
            ChildView()
            
            Divider()
            
            // 自定义环境变量（红色）
            ChildView()
                .environment(\.customTheme, .red)
        }
    }
}

// 预览
#Preview {
    ParentView()
}

struct ParentView: View {
    @State private var dynamicColor: Color = .green
    
    var body: some View {
        VStack {
            ChildView()
                .environment(\.customTheme, dynamicColor)
            
            Button("切换颜色") {
                dynamicColor = [.red, .green, .blue].randomElement()!
            }
        }
    }
}

// 定义可观察对象
class AppSettings: ObservableObject {
    @Published var isDarkMode: Bool = false
}

// 定义环境键
private struct AppSettingsKey: EnvironmentKey {
    static let defaultValue = AppSettings()
}

// 扩展 EnvironmentValues
extension EnvironmentValues {
    var appSettings: AppSettings {
        get { self[AppSettingsKey.self] }
        set { self[AppSettingsKey.self] = newValue }
    }
}

// 使用
struct ContentView: View {
    @Environment(\.appSettings) private var settings
    
    var body: some View {
        Toggle("深色模式", isOn: $settings.isDarkMode)
    }
}