SwiftUI 时间轴PreferenceKey实现方式

SwiftUI 时间轴.swift

import SwiftUI

struct ContentView: View {
    var body: some View {
        NavigationView {
            ScrollView{
                VStack{
                    ForEach(0..<10){_ in
                        TimelineItemView()
                    }
                }
            }
            .navigationTitle("时间轴")
        }
    }
}

struct TimelineItemView: View {
    @State var dividerHeight:CGFloat = 10
    
    var body: some View{
        VStack(alignment: .leading){
            
            HStack(alignment:.top) {
                
                Text("2021-08-25")
                    .frame(height: 50)
                
                VStack {
                    Image(systemName: "calendar.circle.fill")
                        .resizable()
                        .frame(width:50,height: 50)
                        .foregroundColor(.blue)
                    
                    Color.black
                        .frame(width: 5)
                        .frame(height: dividerHeight)
                    
                }
                .foregroundColor(.white)
                
                VStack(alignment: .leading){
                    Text("Demo Title")
                        .font(.title)
                        .frame(height: 50)
                    
                    Text(String(repeating: "测试", count: Int.random(in: 1..<50)))
                        .font(.body)
                        .frame(maxWidth: .infinity,alignment: .leading)
                        .background(
                            GeometryReader{proxy in
                                Color.clear
                                    .preference(key: SizePreferenceKey.self, value: proxy.size)
                            }
                        )
                }
            }
            .onPreferenceChange(SizePreferenceKey.self, perform: { value in
                dividerHeight = value.height
            })
            
        }
    }
}

struct SizePreferenceKey:PreferenceKey {
    static var defaultValue: CGSize = .zero
    
    static func reduce(value: inout CGSize, nextValue: () -> CGSize) {
        value = nextValue()
    }
    
    typealias Value = CGSize
}


struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}