带有 ForEach 的 SwiftUI 列表在一个 VStack 中有效，但在第二个 VStack 中无效

Question

我完全不知道为什么我试图在SwiftUI 中创建的列表（带有ForEach）的行为方式是这样的。我有一个ObservedObject，我在检查员中验证了它具有我期望的数据。在第一个VStack 中，我可以使用ForEach 创建列表，它的输出也很好。在第二个VStack 中，我没有得到任何数据输出。

struct WorkoutPreview: View {
  @Environment(\.managedObjectContext) var managedObjectContext
  @ObservedObject var workoutSessionExercises: WorkoutSessionExercises

  var body: some View {
    NavigationView {
      VStack {
        Text("Welcome to your workout! Below are the exercises and bands you've selected for each.")
          .padding()
        Text("We found \(workoutSessionExercises.workoutExercises.count) workouts.")
          .padding()

        // This List (with ForEach) works fine and produces output.
        List {
          ForEach(0..<workoutSessionExercises.workoutExercises.count) { index in
            Text(self.workoutSessionExercises.workoutExercises[index].exerciseName)
          }
        }
      }

      // The exact same List (with ForEach) in this VStack produces no results.
      VStack {
        List {
          ForEach(0..<workoutSessionExercises.workoutExercises.count) { index in
            Text(self.workoutSessionExercises.workoutExercises[index].exerciseName)
          }
        }
      }

      Spacer()
    }
  }
}

Answer 1

问题是您有 2 个 VStack 在视图中不是一个在另一个之下，因此您看不到第二个列表。 要解决您的问题，请将您的 VStack 包装在另一个 VStack 中，例如：

var body: some View {
    NavigationView {
        VStack {   //  <------
            VStack {
                Text("Welcome to your workout! Below are the exercises and bands you've selected for each.").padding()
                Text("We found \(workoutSessionExercises.workoutExercises.count) workouts.").padding()
                // This List (with ForEach) works fine and produces output.
                List {
                    ForEach(0..<workoutSessionExercises.workoutExercises.count) { index in
                        Text(self.workoutSessionExercises.workoutExercises[index].exerciseName)
                    }
                }
            }
            // The exact same List (with ForEach) in this VStack produces no results.
            VStack {
                List {
                    ForEach(0..<workoutSessionExercises.workoutExercises.count) { index in
                        Text(self.workoutSessionExercises.workoutExercises[index].exerciseName)
                    }
                }
            }
            Spacer()
        }         //  <------
    }
}