[2]SwiftUI

将UIView转化为SwiftUIView

遵循UIViewRepresentable协议再完成makeUIView和updateUIView两个函数

struct MapView: UIViewRepresentable {
    
    func makeUIView(context: Context) -> MKMapView { MKMapView() }
    //给定一个View，根据updateUIView更新View

    func updateUIView(_ uiView: MKMapView, context: Context) { }
    //记录更新的视图
}

Image
自定义形状，显示的样式

Image(landmark.imageName)
    .resizable()
    .frame(width: 250,height: 250)
    .clipShape(Circle())//裁剪
    .overlay(Circle().stroke(Color.white,lineWidth: 4))//覆盖一个东西
    .shadow(radius: 10)
    .offset(x: 0, y: -130) //移动
    .padding(.bottom,-130)//offset和padding经常灵活使用

Button
显示的形式和action

Button(action: {
    self.userData.userLandmarks[self.landmarkIndex].isFavorite.toggle()
    }){
        if userData.userLandmarks[landmarkIndex].isFavorite {
       Image(systemName: "star.fill")
           .foregroundColor(.yellow)
      }else{
       Image(systemName:"star")
       .foregroundColor(.gray)
      }

ForEach和List

在list中加其他元素可以用ForEach将数据打包

List{
                
 Toggle(isOn: $showFavoritesOnly) {
      Text("只展示收藏")
  }
                
  //在list中加其他元素可以用ForEach将数据打包
 ForEach(userData.userLandmarks) { landmark in
    if !self.showFavoritesOnly || landmark.isFavorite{
        NavigationLink(
            destination: LandmarkDetail(landmark: landmark).environmentObject(self.userData)
                      ){
             LandmarkCell(landmark: landmark)
   		 }
    }

Preview

利用Group可以显示多个不同的数据

struct LandmarkCell_Previews: PreviewProvider {
    static var previews: some View {
        Group{
            LandmarkCell(landmark: landmarks[1])
            LandmarkCell(landmark: landmarks[2])
            LandmarkCell(landmark: landmarks[3])
            LandmarkCell(landmark: landmarks[4])
        }
        .previewLayout(.fixed(width: 300, height: 70))//显示的大小

    }
}

ObservableObject

//单个变量用@State一个数组用@EnvironmentObject

1.创建UserData类

import SwiftUI
import Combine

//单个变量用@State一个数组用ObservableObject
final class UserData: ObservableObject  {
    //当数据变化时发送更新后的数据给视图，视图就会刷新
    @Published var userLandmarks = landmarks
}

2.在页面生成前就实例化环境变量（SceneDelegate）

if let windowScene = scene as? UIWindowScene {
   let window = UIWindow(windowScene: windowScene)
   window.rootViewController = UIHostingController(rootView: contentView.environmentObject(UserData()))
   //在程序一开始就马上实例化环境变量
   self.window = window
   window.makeKeyAndVisible()
}

3.创建环境变量

    @EnvironmentObject var userData: UserData

4.确定的Index

var landmarkIndex: Int{
  	userData.userLandmarks.firstIndex(where: {$0.id == landmark.id})!
}