import UIKit
class ImageCache {
static let shared = ImageCache()
private let cache = NSCache<NSString, UIImage>()
private init() {
cache.countLimit = 100
cache.totalCostLimit = 50 * 1024 * 1024 // 50 MB
}
func get(forKey key: String) -> UIImage? {
return cache.object(forKey: key as NSString)
}
func set(_ image: UIImage, forKey key: String) {
cache.setObject(image, forKey: key as NSString)
}
func remove(forKey key: String) {
cache.removeObject(forKey: key as NSString)
}
func removeAll() {
cache.removeAllObjects()
}
}
class ImageLoader: ObservableObject {
@Published var image: UIImage?
@Published var isLoading = false
private let url: URL
private let cache = ImageCache.shared
init(url: URL) {
self.url = url
}
@MainActor
func load() async {
let urlString = url.absoluteString
// Check cache first
if let cached = cache.get(forKey: urlString) {
image = cached
return
}
isLoading = true
do {
let (data, _) = try await URLSession.shared.data(from: url)
if let downloadedImage = UIImage(data: data) {
cache.set(downloadedImage, forKey: urlString)
image = downloadedImage
}
} catch {
print("Failed to load image: \(error)")
}
isLoading = false
}
}
import SwiftUI
struct CachedAsyncImage<Content: View, Placeholder: View>: View {
let url: URL
let content: (Image) -> Content
let placeholder: () -> Placeholder
@StateObject private var loader: ImageLoader
init(
url: URL,
@ViewBuilder content: @escaping (Image) -> Content,
@ViewBuilder placeholder: @escaping () -> Placeholder
) {
self.url = url
self.content = content
self.placeholder = placeholder
_loader = StateObject(wrappedValue: ImageLoader(url: url))
}
var body: some View {
Group {
if let uiImage = loader.image {
content(Image(uiImage: uiImage))
} else {
placeholder()
}
}
.task {
await loader.load()
}
}
}
// Convenience initializer
extension CachedAsyncImage where Content == Image, Placeholder == ProgressView<EmptyView, EmptyView> {
init(url: URL) {
self.init(
url: url,
content: { image in
image
.resizable()
.aspectRatio(contentMode: .fill)
},
placeholder: {
ProgressView()
}
)
}
}
// Usage example
struct PostImageView: View {
let imageURL: URL
var body: some View {
CachedAsyncImage(url: imageURL) { image in
image
.resizable()
.aspectRatio(contentMode: .fill)
.frame(height: 200)
.clipped()
} placeholder: {
Rectangle()
.fill(Color.gray.opacity(0.3))
.frame(height: 200)
.overlay {
ProgressView()
}
}
}
}
Loading images from URLs requires caching to avoid redundant network calls and improve performance. I create an image cache using NSCache which automatically evicts objects under memory pressure. The cache stores UIImage or Data keyed by URL. For async loading, I use URLSession.shared.data(from:) with async/await. SwiftUI's AsyncImage handles loading states but doesn't cache—I build a custom CachedAsyncImage view that checks cache before loading. Prefetching images for list items improves perceived performance. For complex image pipelines with transforms and placeholders, libraries like Kingfisher or SDWebImage help, but a simple cache covers most needs.
