SwiftUI 官方教程（七）

7. 给子 View 传递数据

LandmarkDetail 现在依然使用硬编码的数据来显示地标。像 LandmarkRow 一样，LandmarkDetail 类型和它组合的其他 view 都需要一个 landmark 属性作为它们的数据源。

在开始子 view 的内容时，我们会把 CircleImage 、 MapView 和 LandmarkDetail 的显示从硬编码改为传入的数据。SwiftUI 官方教程

7.1 在 CircleImage.swif 中，添加存储属性 image 。SwiftUI教程

这是使用 SwiftUI 构建 view 时的常见模式。我们的自定义 view 通常会为特定视图包装和封装一些 modifiers 。

CircleImage.swift

import SwiftUI

struct CircleImage: View {
    var image: Image

    var body: some View {
        image
            .clipShape(Circle())
            .overlay(Circle().stroke(Color.white, lineWidth: 4))
            .shadow(radius: 10)
    }
}

struct CircleImage_Preview: PreviewProvider {
    static var previews: some View {
        CircleImage()
    }
}

7.2 更新 preview provider ，传递一个 Turtle Rock 的图片。

CircleImage.swift

import SwiftUI

struct CircleImage: View {
    var image: Image

    var body: some View {
        image
            .clipShape(Circle())
            .overlay(Circle().stroke(Color.white, lineWidth: 4))
            .shadow(radius: 10)
    }
}

struct CircleImage_Preview: PreviewProvider {
    static var previews: some View {
        CircleImage(image: Image("turtlerock"))
    }
}

7.3 在 MapView.swift 中，给 MapView 添加一个 coordinate 属性，然后把经纬度的硬编码换成使用这个属性。SwiftUI教程

MapView.swift

import SwiftUI
import MapKit

struct MapView: UIViewRepresentable {
    var coordinate: CLLocationCoordinate2D

    func makeUIView(context: Context) -> MKMapView {
        MKMapView(frame: .zero)
    }

    func updateUIView(_ view: MKMapView, context: Context) {

        let span = MKCoordinateSpan(latitudeDelta: 0.02, longitudeDelta: 0.02)
        let region = MKCoordinateRegion(center: coordinate, span: span)
        view.setRegion(region, animated: true)
    }
}

struct MapView_Preview: PreviewProvider {
    static var previews: some View {
        MapView()
    }
}

7.4 更新 preview provider ，传递数据数组中第一个地标的坐标。

MapView.swift

import SwiftUI
import MapKit

struct MapView: UIViewRepresentable {
    var coordinate: CLLocationCoordinate2D

    func makeUIView(context: Context) -> MKMapView {
        MKMapView(frame: .zero)
    }

    func updateUIView(_ view: MKMapView, context: Context) {
        let span = MKCoordinateSpan(latitudeDelta: 0.02, longitudeDelta: 0.02)
        let region = MKCoordinateRegion(center: coordinate, span: span)
        view.setRegion(region, animated: true)
    }
}

struct MapView_Preview: PreviewProvider {
    static var previews: some View {
        MapView(coordinate: landmarkData[0].locationCoordinate)
    }
}

7.5 在 LandmarkDetail.swift 中，SwiftUI教程 给 LandmarkDetail 类型添加 landmark 属性。

LandmarkDetail.swift

import SwiftUI

struct LandmarkDetail: View {
    var landmark: Landmark

    var body: some View {
        VStack {
            MapView()
                .frame(height: 300)

            CircleImage()
                .offset(y: -130)
                .padding(.bottom, -130)

            VStack(alignment: .leading) {
                Text("Turtle Rock")
                    .font(.title)

                HStack(alignment: .top) {
                    Text("Joshua Tree National Park")
                        .font(.subheadline)
                    Spacer()
                    Text("California")
                        .font(.subheadline)
                }
            }
            .padding()

            Spacer()
        }
    }
}

struct LandmarkDetail_Preview: PreviewProvider {
    static var previews: some View {
        LandmarkDetail()
    }
}

7.6 更新 preview provider ，使用 landmarkData 中的第一个地标。

LandmarkDetail.swift

import SwiftUI

struct LandmarkDetail: View {
    var landmark: Landmark

    var body: some View {
        VStack {
            MapView()
                .frame(height: 300)

            CircleImage()
                .offset(y: -130)
                .padding(.bottom, -130)

            VStack(alignment: .leading) {
                Text("Turtle Rock")
                    .font(.title)

                HStack(alignment: .top) {
                    Text("Joshua Tree National Park")
                        .font(.subheadline)
                    Spacer()
                    Text("California")
                        .font(.subheadline)
                }
            }
            .padding()

            Spacer()
        }
    }
}

struct LandmarkDetail_Preview: PreviewProvider {
    static var previews: some View {
        LandmarkDetail(landmark: landmarkData[0])
    }
}

7.7 将所需数据传递给我们的自定义类型。

LandmarkDetail.swift

import SwiftUI

struct LandmarkDetail: View {
    var landmark: Landmark

    var body: some View {
        VStack {
            MapView(coordinate: landmark.locationCoordinate)
                .frame(height: 300)

            CircleImage(image: landmark.image(forSize: 250))
                .offset(y: -130)
                .padding(.bottom, -130)

            VStack(alignment: .leading) {
                Text(landmark.name)
                    .font(.title)

                HStack(alignment: .top) {
                    Text(landmark.park)
                        .font(.subheadline)
                    Spacer()
                    Text(landmark.state)
                        .font(.subheadline)
                }
            }
            .padding()

            Spacer()
        }
    }
}

struct LandmarkDetail_Preview: PreviewProvider {
    static var previews: some View {
        LandmarkDetail(landmark: landmarkData[0])
    }
}

7.8 最后，调用 navigationBarTitle(_:displayMode:) 方法，给导航栏添加显示详情 view 时的标题。

LandmarkDetail.swift

import SwiftUI

struct LandmarkDetail: View {
    var landmark: Landmark

    var body: some View {
        VStack {
            MapView(coordinate: landmark.locationCoordinate)
                .frame(height: 300)

            CircleImage(image: landmark.image(forSize: 250))
                .offset(y: -130)
                .padding(.bottom, -130)

            VStack(alignment: .leading) {
                Text(landmark.name)
                    .font(.title)

                HStack(alignment: .top) {
                    Text(landmark.park)
                        .font(.subheadline)
                    Spacer()
                    Text(landmark.state)
                        .font(.subheadline)
                }
            }
            .padding()

            Spacer()
        }
        .navigationBarTitle(Text(landmark.name), displayMode: .inline)
    }
}

struct LandmarkDetail_Preview: PreviewProvider {
    static var previews: some View {
        LandmarkDetail(landmark: landmarkData[0])
    }
}

7.9 在 SceneDelegate.swift 中，把 app 的 rootView 改成 LandmarkList 。

当我们不使用预览而是在模拟器中独立运行 app 时，app 会以 SceneDelegate 中定义的 rootView开始显示。

SceneDelegate.swift

import UIKit
import SwiftUI

class SceneDelegate: UIResponder, UIWindowSceneDelegate {
    var window: UIWindow?

    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
        // Use this method to optionally configure and attach the UIWindow `window` to the provided UIWindowScene `scene`.
        // If using a storyboard, the `window` property will automatically be initialized and attached to the scene.
        // This delegate does not imply the connecting scene or session are new (see `application:configurationForConnectingSceneSession` instead).

        // Use a UIHostingController as window root view controller
        let window = UIWindow(frame: UIScreen.main.bounds)
        window.rootViewController = UIHostingController(rootView: LandmarkList())
        self.window = window
        window.makeKeyAndVisible()
    }

    // ...
}

7.10 在 LandmarkList.swift 中，给目标 LandmarkDetail 传递当前的地标。

LandmarkList.swift

import SwiftUI

struct LandmarkList: View {
    var body: some View {
        NavigationView {
            List(landmarkData) { landmark in
                NavigationButton(destination: LandmarkDetail(landmark: landmark)) {
                    LandmarkRow(landmark: landmark)
                }
            }
            .navigationBarTitle(Text("Landmarks"))
        }
    }
}

struct LandmarkList_Previews: PreviewProvider {
    static var previews: some View {
        LandmarkList()
    }
}

7.11 切换到实时预览，可以查看从列表导航到正确的地标详情 view 了。