无法在此文件中预览-SwiftUI

Question

我是SwiftUI的新手，正在尝试查看文件的预览。当我运行文件时，它说构建成功，但未显示预览。我一直在寻找解决该问题的方法，并尝试了诸如更新Xcode，创建新文件等操作。我该如何解决？

这是我的代码。

import SwiftUI

struct ChooseGoalsView: View {
@State var goals = goalCardData
@State var active = false
@State var activeIndex = -1
@State var activeView = CGSize.zero

var body: some View {
    ZStack {
        Color.black.opacity(Double(self.activeView.height/500))
            .animation(.linear)
            .edgesIgnoringSafeArea(.all)
        
        ScrollView {
            VStack(spacing: 25) {
                HStack {
                    Image(uiImage: #imageLiteral(resourceName: "back"))
                        .foregroundColor(Color("Dark Grey"))
                    
                    Text("Choose")
                        .font(.custom("PlayfairDisplay-Bold", size: 36))
                        .foregroundColor(Color("Dark Blue"))
                    
                    Text("a category")
                        .font(.custom("PlayfairDisplay-Regular", size: 36))
                        .foregroundColor(Color("Grey"))
                }
                .frame(maxWidth: .infinity, alignment: .leading)
                .padding(.leading, 30)
                .padding(.top, 30)
                .blur(radius: active ? 20 : 0)
                
                ForEach(goals.indices, id: \.self) { index in
                    GeometryReader { geometry in
                        GoalsView(
                            show: self.$goals[index].show,
                            goal: self.goals[index],
                            active: self.$active,
                            index: index,
                            activeIndex: self.$activeIndex,
                            activeView: self.$activeView
                        )
                            .offset(y: self.goals[index].show ? -geometry.frame(in: .global).minY : 0)
                            .opacity(self.activeIndex != index && self.active ? 0 : 1)
                            .scaleEffect(self.activeIndex != index && self.active ? 0.5 : 1)
                            .offset(x: self.activeIndex != index && self.active ? screen.width : 0)
                    }
                    .frame(height: 280)
                    .frame(maxWidth: self.goals[index].show ? .infinity : screen.width - 60)
                    .zIndex(self.goals[index].show ? 1 : 0)
                }
            }
            .frame(width: screen.width)
            .animation(.spring(response: 0.5, dampingFraction: 0.6, blendDuration: 0))
        }
        .statusBar(hidden: active ? true : false)
        .animation(.linear)
    }
}
}

#if DEBUG
struct ChooseGoalsView_Previews: PreviewProvider {
static var previews: some View {
    ChooseGoalsView()
}
}
#endif

struct GoalsView: View {
@Binding var show: Bool
var goal: GoalsCards
@Binding var active: Bool
var index: Int
@Binding var activeIndex: Int
@Binding var activeView: CGSize

var body: some View {
    ZStack(alignment: .top) {
        VStack(alignment: .leading) {
            Text(goal.description)
                .font(.custom("PlayfairDisplay-Regular", size: 20))
                .foregroundColor(Color("Dark Text"))
            
            Button(action: {}) {
                
                Text("Get Involved")
                    .background(Color(goal.color))
                    .font(.custom("PlayfairDisplay-Bold", size: 18))
                    .foregroundColor(Color("Dark Text"))
                    .offset(x: screen.width - 200, y: 50)
            }
        }
        .padding(30)
        .frame(maxWidth: show ? .infinity : screen.width - 60, maxHeight: show ? .infinity : 280, alignment: .top)
        .offset(y: show ? 375 : 0)
        .background(Color.white)
        .clipShape(RoundedRectangle(cornerRadius: 30, style: .continuous))
        .shadow(color: Color.black.opacity(0.2), radius: 20, x: 0, y: 20)
        .opacity(show ? 1 : 0)
        
        VStack {
            HStack(alignment: .top) {
                Text(goal.title)
                    .font(.custom("PlayfairDisplay-Bold", size: 34))
                    .foregroundColor(.white)
                Spacer()
                    VStack {
                        Image(systemName: "xmark")
                            .font(.system(size: 16, weight: .medium))
                            .foregroundColor(.white)
                    }
                    .frame(width: 36, height: 36)
                    .background(Color.black)
                    .clipShape(Circle())
                    .opacity(show ? 1 : 0)
            }
            Spacer()
            Image(uiImage: goal.image)
                .resizable()
                .aspectRatio(contentMode: .fit)
                .frame(maxWidth: .infinity)
                .frame(height: 140, alignment: .top)
        }
        .padding(show ? 30 : 20)
        .padding(.top, show ? 30 : 0)
        .frame(maxWidth: show ? .infinity : screen.width - 60, maxHeight: show ? 375 : 280)
            .background(Color(goal.color))
        .clipShape(RoundedRectangle(cornerRadius: 30, style: .continuous))
            .shadow(color: Color(goal.color).opacity(0.3), radius: 20, x: 0, y: 20)
        .gesture(
            show ?
            DragGesture().onChanged { value in
                guard value.translation.height < 300 else { return }
                guard value.translation.height > 0 else { return }
                
                self.activeView = value.translation
            }
            .onEnded { value in
                if self.activeView.height > 50 {
                    self.show = false
                    self.active = false
                    self.activeIndex = -1
                }
                self.activeView = .zero
            }
            : nil
        )
        .onTapGesture {
            self.show.toggle()
            self.active.toggle()
            if self.show {
                self.activeIndex = self.index
            } else {
                self.activeIndex = -1
            }
        }
    }
    .frame(height: show ? screen.height : 280)
    .scaleEffect(1 - self.activeView.height / 1000)
    .rotation3DEffect(Angle(degrees: Double(self.activeView.height / 10)), axis: (x: 0, y: 10.0, z: 0))
    .hueRotation(Angle(degrees: Double(self.activeView.height)))
    .animation(.spring(response: 0.5, dampingFraction: 0.6, blendDuration: 0))
    .gesture(
        show ?
        DragGesture().onChanged { value in
            guard value.translation.height < 300 else { return }
            guard value.translation.height > 0 else { return }
            
            self.activeView = value.translation
        }
        .onEnded { value in
            if self.activeView.height > 50 {
                self.show = false
                self.active = false
                self.activeIndex = -1
            }
            self.activeView = .zero
        }
        : nil
    )
    .edgesIgnoringSafeArea(.all)
}
}

struct GoalsCards: Identifiable {
var id = UUID()
var title: String
var image: UIImage
var color: UIColor
var show: Bool
var description: String
}

var goalCardData = [
GoalsCards(title: "One", image: #imageLiteral(resourceName: "Frame 1"), color: #colorLiteral(red: 0.4941176471, green: 0.8, blue: 0.6235294118, alpha: 1), show: false, description: "This is the first goal."),
GoalsCards(title: "Two", image: #imageLiteral(resourceName: "Frame 2"), color: #colorLiteral(red: 0.8156862745, green: 0.9529411765, blue: 0.8666666667, alpha: 1), show: false, description: "This is the second goal.")]

let screen = UIScreen.main.bounds