如何將 UIImage 異步加載到 SwiftUI Image 中？

Question

在 SwiftUI 中，有一些.init方法可以創建圖像，但它們都不允許使用塊或任何其他方式從網絡/緩存加載 UIImage ......

我正在使用Kingfisher從網絡加載圖像並緩存在列表行中，但是在視圖中繪制圖像的方法是再次重新渲染它，我不想這樣做。 此外，我正在創建一個假圖像（僅彩色）作為占位符，同時獲取圖像。 另一種方法是將所有內容都包裝在自定義視圖中，並且僅重新渲染包裝器。 不過我還沒試過。

此示例現在正在運行。 任何改進當前的想法都會很棒

使用加載器的一些視圖

struct SampleView : View {

    @ObjectBinding let imageLoader: ImageLoader

    init(imageLoader: ImageLoader) {
        self.imageLoader = imageLoader
    }

    var body: some View {
       Image(uiImage: imageLoader.image(for: "https://url-for-image"))
          .frame(width: 128, height: 128)
          .aspectRatio(contentMode: ContentMode.fit)
    }

}

import UIKit.UIImage
import SwiftUI
import Combine
import class Kingfisher.ImageDownloader
import struct Kingfisher.DownloadTask
import class Kingfisher.ImageCache
import class Kingfisher.KingfisherManager

class ImageLoader: BindableObject {

    var didChange = PassthroughSubject<ImageLoader, Never>()
    private let downloader: ImageDownloader
    private let cache: ImageCache
    private var image: UIImage? {
        didSet {
            dispatchqueue.async { [weak self] in
                guard let self = self else { return }
                self.didChange.send(self)
            }
        }
    }
    private var task: DownloadTask?
    private let dispatchqueue: DispatchQueue

    init(downloader: ImageDownloader = KingfisherManager.shared.downloader,
         cache: ImageCache = KingfisherManager.shared.cache,
         dispatchqueue: DispatchQueue = DispatchQueue.main) {
        self.downloader = downloader
        self.cache = cache
        self.dispatchqueue = dispatchqueue
    }

    deinit {
        task?.cancel()
    }

    func image(for url: URL?) -> UIImage {
        guard let targetUrl = url else {
            return UIImage.from(color: .gray)
        }
        guard let image = image else {
            load(url: targetUrl)
            return UIImage.from(color: .gray)
        }
        return image
    }

    private func load(url: URL) {
        let key = url.absoluteString
        if cache.isCached(forKey: key) {
            cache.retrieveImage(forKey: key) {  [weak self] (result) in
                guard let self = self else { return }
                switch result {
                case .success(let value):
                    self.image = value.image
                case .failure(let error):
                    print(error.localizedDescription)
                }
            }
        } else {
            downloader.downloadImage(with: url, options: nil, progressBlock: nil) {  [weak self] (result) in
                guard let self = self else { return }
                switch result {
                case .success(let value):
                    self.cache.storeToDisk(value.originalData, forKey: url.absoluteString)
                    self.image = value.image
                case .failure(let error):
                    print(error.localizedDescription)
                }
            }
        }
    }

}

Answer 1

將您的模型傳遞給包含 url 的 ImageRow 結構。

import SwiftUI
import Combine

struct ContentView : View {
    var listData: Post
    var body: some View {
        List(model.post) { post in
            ImageRow(model: post) // Get image
        }
    }
}

/********************************************************************/
// Download Image

struct ImageRow: View {
    let model: Post
    var body: some View {
        VStack(alignment: .center) {
            ImageViewContainer(imageUrl: model.avatar_url)
        }
    }
}

struct ImageViewContainer: View {
    @ObjectBinding var remoteImageURL: RemoteImageURL

    init(imageUrl: String) {
        remoteImageURL = RemoteImageURL(imageURL: imageUrl)
    }

    var body: some View {
        Image(uiImage: UIImage(data: remoteImageURL.data) ?? UIImage())
            .resizable()
            .clipShape(Circle())
            .overlay(Circle().stroke(Color.black, lineWidth: 3.0))
            .frame(width: 70.0, height: 70.0)
    }
}

class RemoteImageURL: BindableObject {
    var didChange = PassthroughSubject<Data, Never>()
    var data = Data() {
        didSet {
            didChange.send(data)
        }
    }
    init(imageURL: String) {
        guard let url = URL(string: imageURL) else { return }

        URLSession.shared.dataTask(with: url) { (data, response, error) in
            guard let data = data else { return }

            DispatchQueue.main.async { self.data = data }

            }.resume()
    }
}
/********************************************************************/

Answer 2

在 SwiftUI 中加載圖像的一種更簡單、更清晰的方法是使用著名的 Kingfisher 庫。

1. 通過 Swift 包管理器添加Kingfisher

選擇文件 > Swift 包 > 添加包依賴。 進入https://github.com/onevcat/Kingfisher.git

在“選擇包存儲庫”對話框中。 在下一頁中，將版本解析規則指定為“Up to Next Major”，最早版本為“5.8.0”。

在 Xcode 檢出源代碼並解析版本后，您可以選擇“KingfisherSwiftUI”庫並將其添加到您的應用程序目標中。

2. import KingfisherSwiftUI
3. KFImage(myUrl)

完畢！ 就這么簡單

Answer 3

SwiftUI 3

從 iOS 15 開始，我們現在可以使用AsyncImage ：

AsyncImage(url: URL(string: "https://example.com/icon.png")) { image in
    image.resizable()
} placeholder: {
    ProgressView()
}
.frame(width: 50, height: 50)

---

SwiftUI 2

這是一個支持緩存和多種加載狀態的原生 SwiftUI 解決方案：

import Combine
import SwiftUI

struct NetworkImage: View {
    @StateObject private var viewModel = ViewModel()

    let url: URL?

    var body: some View {
        Group {
            if let data = viewModel.imageData, let uiImage = UIImage(data: data) {
                Image(uiImage: uiImage)
                    .resizable()
                    .aspectRatio(contentMode: .fit)
            } else if viewModel.isLoading {
                ProgressView()
            } else {
                Image(systemName: "photo")
            }
        }
        .onAppear {
            viewModel.loadImage(from: url)
        }
    }
}

extension NetworkImage {
    class ViewModel: ObservableObject {
        @Published var imageData: Data?
        @Published var isLoading = false

        private static let cache = NSCache<NSURL, NSData>()

        private var cancellables = Set<AnyCancellable>()

        func loadImage(from url: URL?) {
            isLoading = true
            guard let url = url else {
                isLoading = false
                return
            }
            if let data = Self.cache.object(forKey: url as NSURL) {
                imageData = data as Data
                isLoading = false
                return
            }
            URLSession.shared.dataTaskPublisher(for: url)
                .map { $0.data }
                .replaceError(with: nil)
                .receive(on: DispatchQueue.main)
                .sink { [weak self] in
                    if let data = $0 {
                        Self.cache.setObject(data as NSData, forKey: url as NSURL)
                        self?.imageData = data
                    }
                    self?.isLoading = false
                }
                .store(in: &cancellables)
        }
    }
}

（上面的代碼沒有使用任何第三方庫，因此可以很容易地以任何方式更改NetworkImage 。）

---

演示

import Combine
import SwiftUI

struct ContentView: View {
    @State private var showImage = false

    var body: some View {
        if showImage {
            NetworkImage(url: URL(string: "https://stackoverflow.design/assets/img/logos/so/logo-stackoverflow.png"))
                .frame(maxHeight: 150)
                .padding()
        } else {
            Button("Load") {
                showImage = true
            }
        }
    }
}

（我使用了一個特別大的 Stack Overflow 標志來顯示加載狀態。）

Answer 4

將imageLoader定義為@ObjectBinding ：

@ObjectBinding private var imageLoader: ImageLoader

---

使用圖像的 url 初始化視圖會更有意義：

struct SampleView : View {

    var imageUrl: URL

    private var image: UIImage {
        imageLoader.image(for: imageUrl)
    }

    @ObjectBinding private var imageLoader: ImageLoader

    init(url: URL) {
        self.imageUrl = url
        self.imageLoader = ImageLoader()
    }

    var body: some View {
        Image(uiImage: image)
            .frame(width: 200, height: 300)
            .aspectRatio(contentMode: ContentMode.fit)
    }
}

例如 ：

//Create a SampleView with an initial photo
var s = SampleView(url: URL(string: "https://placebear.com/200/300")!)
//You could then update the photo by changing the imageUrl
s.imageUrl = URL(string: "https://placebear.com/200/280")!

Answer 5

我只會使用onAppear回調

import Foundation
import SwiftUI
import Combine
import UIKit
    struct ImagePreviewModel {
        var urlString : String
        var width : CGFloat = 100.0
        var height : CGFloat = 100.0
    }

    struct ImagePreview: View {
        let viewModel: ImagePreviewModel
        @State var initialImage = UIImage()
        var body: some View {
            Image(uiImage: initialImage)
                .resizable()
                .aspectRatio(contentMode: .fit)
                .frame(width: self.width, height: self.height)
                .onAppear {
                    guard let url = URL(string: self.viewModel.urlString) else { return }
                    URLSession.shared.dataTask(with: url) { (data, response, error) in
                        guard let data = data else { return }
                        guard let image = UIImage(data: data) else { return }

                        RunLoop.main.perform {
                            self.initialImage = image
                        }

                    }.resume()
                }
        }
        var width: CGFloat { return max(viewModel.width, 100.0) }
        var height: CGFloat { return max(viewModel.height, 100.0) }
    }

Answer 6

import SwiftUI
struct UrlImageView: View {
@ObservedObject var urlImageModel: UrlImageModel

init(urlString: String?) {
    urlImageModel = UrlImageModel(urlString: urlString)
}

var body: some View {
    Image(uiImage: urlImageModel.image ?? UrlImageView.defaultImage!)
        .resizable()
        .scaledToFill()
}

static var defaultImage = UIImage(systemName: "photo")
}

class UrlImageModel: ObservableObject {
@Published var image: UIImage?
var urlString: String?

init(urlString: String?) {
    self.urlString = urlString
    loadImage()
}

func loadImage() {
    loadImageFromUrl()
}

func loadImageFromUrl() {
    guard let urlString = urlString else {
        return
    }
    
    let url = URL(string: urlString)!
    let task = URLSession.shared.dataTask(with: url, completionHandler: 
getImageFromResponse(data:response:error:))
    task.resume()
}


func getImageFromResponse(data: Data?, response: URLResponse?, error: Error?) 
{
    guard error == nil else {
        print("Error: \(error!)")
        return
    }
    guard let data = data else {
        print("No data found")
        return
    }
    
    DispatchQueue.main.async {
        guard let loadedImage = UIImage(data: data) else {
            return
        }
        self.image = loadedImage
    }
}
}

並像這樣使用：

UrlImageView(urlString: "https://developer.apple.com/assets/elements/icons/swiftui/swiftui-96x96_2x.png").frame(width:100, height:100)

Answer 7

隨着 2021 年 iOS 15 和 macOS 12 的發布，SwiftUI 提供了原生的AsyncImage視圖，可以異步加載圖像。 請記住，對於較早的操作系統版本，您仍然必須退回到自定義實現。

AsyncImage(url: URL(string: "https://example.com/tile.png"))

API 本身還提供了多種方式來自定義圖像或提供占位符，例如：

AsyncImage(url: URL(string: "https://example.com/tile.png")) { image in
    image.resizable(resizingMode: .tile)
} placeholder: {
    Color.green
}

更多內容請參閱Apple 開發人員文檔。