FetchImageView

FetchImageView.swift

import SwiftUI
import Nuke

@available(watchOS 7.0, *)
@available(tvOS 14.0, *)
@available(iOS 14.0, *)
@available(OSX 11.0, *)
public struct FetchImageView<Placeholder>: View where Placeholder: View {
    public var body: some View {
        content
            .onAppear {
                if let request = self.request {
                    // Restarts the request if previous download failed
                    fetchImage.fetch(request: request, lowDataRequest: lowDataRequest)
                } else {
                    fetchImage.reset()
                }
                fetchImage.priority = .normal
            }
            .onDisappear {
                fetchImage.priority = .low
            }
    }
    
    /// Initializes the fetch request and immediately start loading.
    public init(request: ImageRequest? = nil, lowDataRequest: ImageRequest? = nil, @ViewBuilder placeholder: () -> Placeholder) {
        self.placeholder = placeholder()
        self.request = request
        self.lowDataRequest = lowDataRequest
    }

    /// Initializes the fetch request and immediately start loading.
    public init(url: URL, @ViewBuilder placeholder: () -> Placeholder) {
        self.init(request: ImageRequest(url: url), placeholder: placeholder)
    }

    /// A convenience initializer that fetches the image with a regular URL with
    /// constrained network access disabled, and if the download fails because of
    /// the constrained network access, uses a low data URL instead.
    public init(regularUrl: URL, lowDataUrl: URL, @ViewBuilder placeholder: () -> Placeholder) {
        var request = URLRequest(url: regularUrl)
        request.allowsConstrainedNetworkAccess = false

        self.init(request: ImageRequest(urlRequest: request), lowDataRequest: ImageRequest(url: lowDataUrl), placeholder: placeholder)
    }
    
    @StateObject
    private var fetchImage = FetchImage()
    private var request: ImageRequest?
    private var lowDataRequest: ImageRequest?
    private var placeholder: Placeholder
    
    @ViewBuilder
    private var content: some View {
        if let fetchedImage = fetchImage.image {
            #if os(macOS)
            Image(nsImage: fetchedImage)
            #else
            Image(uiImage: fetchedImage)
            #endif
        } else {
            placeholder
        }
    }
}

@available(watchOS 7.0, *)
@available(tvOS 14.0, *)
@available(iOS 14.0, *)
@available(OSX 11.0, *)
public extension FetchImageView where Placeholder == Color {
    /// Initializes the fetch request and immediately start loading.
    init(request: ImageRequest? = nil, lowDataRequest: ImageRequest? = nil) {
        self.init(request: request, lowDataRequest: lowDataRequest) {
            Color.white
        }
    }

    /// Initializes the fetch request and immediately start loading.
    init(url: URL) {
        self.init(url: url) {
            Color.white
        }
    }

    /// A convenience initializer that fetches the image with a regular URL with
    /// constrained network access disabled, and if the download fails because of
    /// the constrained network access, uses a low data URL instead.
    init(regularUrl: URL, lowDataUrl: URL) {
        self.init(regularUrl: regularUrl, lowDataUrl: lowDataUrl) {
            Color.white
        }
    }
}

#if DEBUG
@available(watchOS 7.0, *)
@available(tvOS 14.0, *)
@available(iOS 14.0, *)
@available(OSX 11.0, *)
struct FetchImageView_Previews: PreviewProvider {
    static var previews: some View {
        FetchImageView(url: URL(string: "https://cloud.githubusercontent.com/assets/1567433/13918338/f8670eea-ef7f-11e5-814d-f15bdfd6b2c0.png")!) {
            Text("Loading...")
        }
    }
}
#endif