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Pods/Kingfisher/Sources/SwiftUI/ImageBinder.swift

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+//
+//  ImageBinder.swift
+//  Kingfisher
+//
+//  Created by onevcat on 2019/06/27.
+//
+//  Copyright (c) 2019 Wei Wang <onevcat@gmail.com>
+//
+//  Permission is hereby granted, free of charge, to any person obtaining a copy
+//  of this software and associated documentation files (the "Software"), to deal
+//  in the Software without restriction, including without limitation the rights
+//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+//  copies of the Software, and to permit persons to whom the Software is
+//  furnished to do so, subject to the following conditions:
+//
+//  The above copyright notice and this permission notice shall be included in
+//  all copies or substantial portions of the Software.
+//
+//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+//  THE SOFTWARE.
+
+#if canImport(SwiftUI) && canImport(Combine)
+import SwiftUI
+import Combine
+
+@available(iOS 14.0, macOS 11.0, tvOS 14.0, watchOS 7.0, *)
+extension KFImage {
+
+    /// Represents a binder for `KFImage`. It takes responsibility as an `ObjectBinding` and performs
+    /// image downloading and progress reporting based on `KingfisherManager`.
+    class ImageBinder: ObservableObject {
+        
+        init() {}
+
+        var downloadTask: DownloadTask?
+        private var loading = false
+
+        var loadingOrSucceeded: Bool {
+            return loading || loadedImage != nil
+        }
+
+        // Do not use @Published due to https://github.com/onevcat/Kingfisher/issues/1717. Revert to @Published once
+        // we can drop iOS 12.
+        private(set) var loaded = false
+
+        private(set) var animating = false
+
+        var loadedImage: KFCrossPlatformImage? = nil { willSet { objectWillChange.send() } }
+        var progress: Progress = .init()
+
+        func markLoading() {
+            loading = true
+        }
+
+        func markLoaded(sendChangeEvent: Bool) {
+            loaded = true
+            if sendChangeEvent {
+                objectWillChange.send()
+            }
+        }
+
+        func start<HoldingView: KFImageHoldingView>(context: Context<HoldingView>) {
+            guard let source = context.source else {
+                CallbackQueue.mainCurrentOrAsync.execute {
+                    context.onFailureDelegate.call(KingfisherError.imageSettingError(reason: .emptySource))
+                    if let image = context.options.onFailureImage {
+                        self.loadedImage = image
+                    }
+                    self.loading = false
+                    self.markLoaded(sendChangeEvent: false)
+                }
+                return
+            }
+
+            loading = true
+            
+            progress = .init()
+            downloadTask = KingfisherManager.shared
+                .retrieveImage(
+                    with: source,
+                    options: context.options,
+                    progressBlock: { size, total in
+                        self.updateProgress(downloaded: size, total: total)
+                        context.onProgressDelegate.call((size, total))
+                    },
+                    completionHandler: { [weak self] result in
+
+                        guard let self = self else { return }
+
+                        CallbackQueue.mainCurrentOrAsync.execute {
+                            self.downloadTask = nil
+                            self.loading = false
+                        }
+                        
+                        switch result {
+                        case .success(let value):
+                            CallbackQueue.mainCurrentOrAsync.execute {
+                                if let fadeDuration = context.fadeTransitionDuration(cacheType: value.cacheType) {
+                                    self.animating = true
+                                    let animation = Animation.linear(duration: fadeDuration)
+                                    withAnimation(animation) {
+                                        // Trigger the view render to apply the animation.
+                                        self.markLoaded(sendChangeEvent: true)
+                                    }
+                                } else {
+                                    self.markLoaded(sendChangeEvent: false)
+                                }
+                                self.loadedImage = value.image
+                                self.animating = false
+                            }
+
+                            CallbackQueue.mainAsync.execute {
+                                context.onSuccessDelegate.call(value)
+                            }
+                        case .failure(let error):
+                            CallbackQueue.mainCurrentOrAsync.execute {
+                                if let image = context.options.onFailureImage {
+                                    self.loadedImage = image
+                                }
+                                self.markLoaded(sendChangeEvent: true)
+                            }
+                            
+                            CallbackQueue.mainAsync.execute {
+                                context.onFailureDelegate.call(error)
+                            }
+                        }
+                })
+        }
+        
+        private func updateProgress(downloaded: Int64, total: Int64) {
+            progress.totalUnitCount = total
+            progress.completedUnitCount = downloaded
+            objectWillChange.send()
+        }
+
+        /// Cancels the download task if it is in progress.
+        func cancel() {
+            downloadTask?.cancel()
+            downloadTask = nil
+            loading = false
+        }
+    }
+}
+#endif