SwiftUI中dismiss环境变量替代方案求助：解决视图重渲染问题

当使用@Environment(\.dismiss)遇到_dismiss频繁变更导致视图重复计算、.task触发异常的iOS已知bug时，可以用以下几种替代方法关闭模态视图：

1. 绑定变量控制模态显隐 #

这是最直观的方案，通过父视图的绑定布尔值直接控制模态的展示与关闭，完全避开系统dismiss环境变量的问题。

// 父视图
struct ParentView: View {
    @State private var isModalPresented = false
    
    var body: some View {
        Button("打开模态") {
            isModalPresented = true
        }
        .sheet(isPresented: $isModalPresented) {
            ModalChildView(isPresented: $isModalPresented)
        }
    }
}

// 模态子视图
struct ModalChildView: View {
    @Binding var isPresented: Bool
    
    var body: some View {
        Button("关闭模态") {
            isPresented = false
        }
    }
}

2. 自定义环境键传递关闭动作 #

如果不想直接传递绑定变量，可以自定义环境键，将关闭动作注入到环境中，用法和系统dismiss类似，但不会触发bug。

// 自定义环境键
private struct CustomDismissKey: EnvironmentKey {
    static let defaultValue: () -> Void = {}
}

extension EnvironmentValues {
    var customDismiss: () -> Void {
        get { self[CustomDismissKey.self] }
        set { self[CustomDismissKey.self] = newValue }
    }
}

// 父视图
struct ParentView: View {
    @State private var isModalPresented = false
    
    var body: some View {
        Button("打开模态") {
            isModalPresented = true
        }
        .sheet(isPresented: $isModalPresented) {
            ModalChildView()
                .environment(\.customDismiss) {
                    isModalPresented = false
                }
        }
    }
}

// 模态子视图
struct ModalChildView: View {
    @Environment(\.customDismiss) private var customDismiss
    
    var body: some View {
        Button("关闭模态") {
            customDismiss()
        }
    }
}

3. ObservableObject 管理模态状态 #

针对复杂页面场景，可以用ObservableObject集中管理模态状态，子视图通过观察该对象执行关闭操作。

class ModalManager: ObservableObject {
    @Published var isModalPresented = false
    
    func dismissModal() {
        isModalPresented = false
    }
}

// 父视图
struct ParentView: View {
    @StateObject private var modalManager = ModalManager()
    
    var body: some View {
        Button("打开模态") {
            modalManager.isModalPresented = true
        }
        .sheet(isPresented: $modalManager.isModalPresented) {
            ModalChildView(manager: modalManager)
        }
    }
}

// 模态子视图
struct ModalChildView: View {
    @ObservedObject var manager: ModalManager
    
    var body: some View {
        Button("关闭模态") {
            manager.dismissModal()
        }
    }
}

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