SwiftUI Sheet默认以Medium打开，支持切换Small/Large的实现方法

要实现Sheet默认以.medium打开，同时支持切换.small和.large尺寸，核心是利用presentationDetents(_:selection:)的绑定重载版本，通过状态变量控制默认选中的detent。具体实现步骤如下：

• 新增一个@State变量存储当前激活的detent，初始值设为.medium：

  @State private var selectedDetent: PresentationDetent = .medium
  

• 修改Sheet的presentationDetents调用，传入包含.small、.medium、.large的尺寸数组，并绑定到上述状态变量：

  .sheet(isPresented: $showUserRegisterSheet) {
      RegisterUserSheetView()
          .presentationDetents([.small, .medium, .large], selection: $selectedDetent)
  }
  

这样设置后，Sheet打开时会默认以.medium尺寸展示，用户可通过拖拽或自定义控件切换到其他尺寸。如果需要在Sheet内部添加切换按钮，只需将selectedDetent以@Binding形式传递给子视图即可。

完整修改后的代码示例 #

@State private var showUserRegisterSheet = false
@State private var selectedDetent: PresentationDetent = .medium

private var userCreateAccount: some View {
    VStack(alignment: .center) {
        Text("New MapGliders? [Create Account](user-register)")
            .font(Font.custom("Nunito-Regular", size: 16))
            .multilineTextAlignment(.center)
            .environment(\.openURL, OpenURLAction { url in
                switch url.absoluteString {
                case "user-register":
                    showUserRegisterSheet = true
                    return .handled
                default:
                    return .discarded
                }
            })
            .sheet(isPresented: $showUserRegisterSheet) {
                RegisterUserSheetView(selectedDetent: $selectedDetent)
                    .presentationDetents([.small, .medium, .large], selection: $selectedDetent)
            }
    }
    .padding(.top, 10)
}

// 子视图示例（如需内部切换尺寸）
struct RegisterUserSheetView: View {
    @Binding var selectedDetent: PresentationDetent
    
    var body: some View {
        VStack(spacing: 20) {
            Button("切换小尺寸") {
                selectedDetent = .small
            }
            Button("切换中尺寸") {
                selectedDetent = .medium
            }
            Button("切换大尺寸") {
                selectedDetent = .large
            }
            // 其他视图内容
        }
        .padding()
    }
}

内容的提问来源于stack exchange，提问作者SLE