如何在SwiftUI中使用枚举控制视图状态

enum ViewState {
    case loading
    case success
    case error
}

@State private var viewState: ViewState = .loading

var body: some View {
    VStack {
        if viewState == .loading {
            Text("Loading...")
        } else if viewState == .success {
            Text("Success!")
        } else if viewState == .error {
            Text("Error occurred.")
        }
    }
}

Button("Load Data") {
    // 模拟异步加载数据
    DispatchQueue.main.asyncAfter(deadline: .now() + 2) {
        viewState = .success
    }
}