Last active
July 21, 2020 17:51
-
-
Save pwightman/d6cf86beb434ab5a81efcb32bcdbf8cd to your computer and use it in GitHub Desktop.
Basic image fetcher, with in-memory cache and request deduplication.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
import Combine | |
import SwiftUI | |
import UIKit | |
struct RemoteImage: View { | |
let url: URL | |
var placeholder: AnyView? | |
@StateObject var fetcher = RemoteImageFetcher() | |
func placeholder<Placeholder: View>(@ViewBuilder _ view: () -> Placeholder) -> RemoteImage { | |
var v = self | |
v.placeholder = AnyView(view()) | |
return v | |
} | |
var body: some View { | |
// Using Group here never triggers onChange/onAppear, presumably because SwiftUI | |
// has some sort of optimization where Group { EmptyView } never renders? Putting | |
// it in a VStack fixes it. | |
VStack { | |
if let image = fetcher.image { | |
Image(uiImage: image) | |
.resizable() | |
.renderingMode(.original) | |
} else if let placeholder = placeholder { | |
placeholder | |
} else { | |
EmptyView() | |
} | |
} | |
.onAppear { | |
fetcher.url = url | |
} | |
.onChange(of: url) { value in | |
fetcher.url = value | |
} | |
} | |
} | |
class RemoteImageFetcher: ObservableObject { | |
@Published var image: UIImage? | |
@Published var url: URL? | |
init() { | |
$url | |
.removeDuplicates() | |
.map { url -> AnyPublisher<UIImage?, Error> in | |
if let url = url { | |
return RemoteImageStore.shared.load(url: url) | |
.eraseToAnyPublisher() | |
} else { | |
return Just(nil) | |
.setFailureType(to: Error.self) | |
.eraseToAnyPublisher() | |
} | |
} | |
.switchToLatest() | |
.replaceError(with: nil) | |
.assign(to: $image) | |
} | |
} | |
class RemoteImageStore { | |
static let shared = RemoteImageStore() | |
let queue = DispatchQueue(label: "com.myapp.RemoteImageStore", qos: .userInitiated) | |
private var subjects: [URL: CurrentValueSubject<UIImage?, Error>] = [:] | |
private var cancellables: [UUID: AnyCancellable] = [:] | |
func load(url: URL) -> AnyPublisher<UIImage?, Error> { | |
if let subject = subjects[url] { | |
return subject.eraseToAnyPublisher() | |
} else { | |
let subject = CurrentValueSubject<UIImage?, Error>(nil) | |
let uuid = UUID() | |
cancellables[uuid] = URLSession.shared.dataTaskPublisher(for: url) | |
.receive(on: queue) | |
.map(\.data) | |
.map { UIImage(data: $0) } | |
.receive(on: DispatchQueue.main) | |
.sink { [weak self] _ in | |
self?.cancellables.removeValue(forKey: uuid)?.cancel() | |
} receiveValue: { [weak subject] image in | |
subject?.send(image) | |
} | |
subjects[url] = subject | |
return subject.eraseToAnyPublisher() | |
} | |
} | |
} |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment