ios - .onAppear 是否导致文本在 SwiftUI 中消失？

Question

我正在做一个简单的倒计时。我期望发生的是First计入 0 ，然后 Second计入 0 .当语句切换到 else block 时，HStack 文本在 Canvas 中消失。为什么会发生这种情况？

import SwiftUI

struct TestCountdown: View {
    @State var first = 5
    @State var second = 5
    @State var totalDuration = 30
    var body: some View {
        VStack {
             Text("\(totalDuration)")
            if (first > 0) && (second > 0) {
                HStack {
                    TestCode(number: $first, title: "First")
                    Spacer()
                    TestCode(number: $second, title: "Second")
                }
            }
        }
        .onAppear {
            Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { _ in
                if self.totalDuration > 0 {
                    self.totalDuration -= 1
                    
                    if self.first > 0 {
                        self.first -= 1
                    } else {
                        self.second -= 1
                    }
                }
            }
        }
    }
}

struct TestCode: View {
    @Binding var number: Int
    @State var title: String
    var body: some View {
        VStack {
            Text(title)
                .font(.system(size: 20, weight: .medium, design: .rounded))
            Text("\(number)")
                .font(.system(size: 30, weight: .medium, design: .rounded))
        }
        .frame(minWidth: 50, maxWidth: .infinity)
    }
}

Answer 1

这意味着您的 HStack将在 时显示两个 first和 second > 0:

if (first > 0) && (second > 0) {
    HStack {
        ...
    }
}

如果要显示HStack当要么 其中 > 0 你可以这样做:

if first > 0 || second > 0 { ... }

请参阅 Apple 文档:

BasicOperators