リスト表示

チュートリアルより

まず静的なJSONのデータ

[
    {
        "name": "Turtle Rock",
        "category": "Featured",
        "city": "Twentynine Palms",
        "state": "California",
        "id": 1001,
        "park": "Joshua Tree National Park",
        "coordinates": {
            "longitude": -116.166868,
            "latitude": 34.011286
        },
        "imageName": "turtlerock"
    },
{...}
]

がある。これをモデルに読み込む。モデルは

import SwiftUI
import CoreLocation

struct Landmark: Hashable, Codable, Identifiable {
    var id: Int
    var name: String
    fileprivate var imageName: String
    fileprivate var coordinates: Coordinates
    var state: String
    var park: String
    var category: Category

    var locationCoordinate: CLLocationCoordinate2D {
        CLLocationCoordinate2D(
            latitude: coordinates.latitude,
            longitude: coordinates.longitude)
    }

    enum Category: String, CaseIterable, Codable, Hashable {
        case featured = "Featured"
        case lakes = "Lakes"
        case rivers = "Rivers"
    }
}

extension Landmark {
    var image: Image {
        ImageStore.shared.image(name: imageName)
    }
}

struct Coordinates: Hashable, Codable {
    var latitude: Double
    var longitude: Double
}

でCodableに対応しているのでそのまま読み込める。 読み込むところはJSONDecoderというのを用いる。

import UIKit
import SwiftUI
import CoreLocation

let landmarkData: [Landmark] = load("landmarkData.json")

func load<T: Decodable>(_ filename: String) -> T {
    let data: Data
    
    guard let file = Bundle.main.url(forResource: filename, withExtension: nil)
        else {
            fatalError("Couldn't find \(filename) in main bundle.")
    }
    
    do {
        data = try Data(contentsOf: file)
    } catch {
        fatalError("Couldn't load \(filename) from main bundle:\n\(error)")
    }
    
    do {
        let decoder = JSONDecoder()
        return try decoder.decode(T.self, from: data)
    } catch {
        fatalError("Couldn't parse \(filename) as \(T.self):\n\(error)")
    }
}

final class ImageStore {
    typealias _ImageDictionary = [String: CGImage]
    fileprivate var images: _ImageDictionary = [:]

    fileprivate static var scale = 2
    
    static var shared = ImageStore()
    
    func image(name: String) -> Image {
        let index = _guaranteeImage(name: name)
        
        return Image(images.values[index], scale: CGFloat(ImageStore.scale), label: Text(name))
    }

    static func loadImage(name: String) -> CGImage {
        guard
            let url = Bundle.main.url(forResource: name, withExtension: "jpg"),
            let imageSource = CGImageSourceCreateWithURL(url as NSURL, nil),
            let image = CGImageSourceCreateImageAtIndex(imageSource, 0, nil)
        else {
            fatalError("Couldn't load image \(name).jpg from main bundle.")
        }
        return image
    }
    
    fileprivate func _guaranteeImage(name: String) -> _ImageDictionary.Index {
        if let index = images.index(forKey: name) { return index }
        
        images[name] = ImageStore.loadImage(name: name)
        return images.index(forKey: name)!
    }
}

リストに表示するセルに対応するものは

import SwiftUI

struct LandmarkRow: View {
    var landmark: Landmark
    var body: some View {
        HStack {
            landmark.image
                .resizable()
                .frame(width: 50, height: 50)
            Text(landmark.name)
            Spacer()
        }
    }
}

struct LandmarkRow_Previews: PreviewProvider {
    static var previews: some View {
        Group {
            LandmarkRow(landmark: landmarkData[0])
            LandmarkRow(landmark: landmarkData[1])
        }
        .previewLayout(.fixed(width: 300, height: 70))

    }
}

のように簡単につくってプレビューもみることができる。 プレビューでは２つのセルを表示していてGroupでまとめてある。 これをリストに表示する。

import SwiftUI

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

struct LandmarkList_Previews: PreviewProvider {
    static var previews: some View {
        ForEach(["iPhone SE","iPhone XS Max"], id: \.self) {
            deviceName in
            LandmarkList()
            .previewDevice(PreviewDevice(rawValue: deviceName))
            .previewDisplayName(deviceName)
        }
    }
}

ここで、プレビューを色々なデバイスで同時にプレビューできるようにしている。 また、NavigationLinkに詳細画面に飛ばしている。その際にデータを渡している点に注目。

詳細画面は

import SwiftUI

struct LandmarkDetail: View {
    
    var landmark:Landmark

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

            CircleImage(image: landmark.image)
                .offset(x: 0, 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_Previews: PreviewProvider {
    static var previews: some View {
        LandmarkDetail(landmark:landmarkData[0])
    }
}