A powerful image loading and caching framework
Swift Other

README.md

A powerful image loading and caching framework which allows for hassle-free image loading in your app - often in one line of code.

Features

Nuke pulls together stable, mature libraries from Swift ecosystem into simple, lightweight package that lets you focus on getting things done.

  • Hassle-free image loading into image views and other targets
  • Two cache layers including LRU memory cache
  • Extensible image transformations
  • Freedom to use networking, caching libraries of your choice
  • Plugins: Alamofire, Gifu, Toucan
  • Automated prefetching with Preheat library
  • Fast (see benchmarks), supports large collection views of images
  • Comprehensive test coverage

Quick Start

Upgrading from the previous version? Use a migration guide.

Usage

Loading Images

Nuke allows for hassle-free image loading into image views and other targets.

Nuke.loadImage(with: url, into: imageView)

Reusing Views

Nuke.loadImage(with:into:) method cancels previous outstanding request associated with the target. No need to implement prepareForReuse. The requests also get cancelled automatically when the target deallocates (Nuke holds a weak reference to a target).

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    Nuke.loadImage(with: url, into: cell.imageView)
}

You can also (optionally) implement collectionView(didEndDisplaying:forItemAt:) method to cancel the request as soon as the cell goes off screen:

func collectionView(_ collectionView: UICollectionView, didEndDisplaying cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
    Nuke.cancelRequest(for: cell.imageView)
}

Customizing Requests

Each image request is represented by Request struct. It can be created with either URL or URLRequest and then further customized.

// Create and customize URLRequest
var urlRequest = URLRequest(url: url)
urlRequest.cachePolicy = .reloadIgnoringLocalCacheData
urlRequest.timeoutInterval = 30

var request = Request(urlRequest: urlRequest)

// You can add arbitrary number of transformations to the request
request.process(with: GaussianBlur())

// Disable memory caching
request.memoryCacheOptions.writeAllowed = false

// Load an image
Nuke.loadImage(with: request, into: imageView)

Custom Handler

Nuke has a flexible loadImage(with request: Request, into target: AnyObject, handler: @escaping Handler) method in which target is a simple reuse token. The method itself doesn't do anything when the image is loaded - you have full control over how to display it, etc. Here's one simple way to use it:

indicator.startAnimating()
Nuke.loadImage(with: request, into: view) { [weak view] in
    view?.handle(response: $0, isFromMemoryCache: $1)
    indicator.stopAnimating()
}

Processing Images

You can specify custom image processors using Processing protocol which consists of a single method process(image: Image) -> Image?. Here's an example of custom image filter that uses Core Image:

struct GaussianBlur: Processing {
    var radius = 8

    func process(image: UIImage) -> UIImage? {
        return image.applyFilter(CIFilter(name: "CIGaussianBlur", withInputParameters: ["inputRadius" : self.radius]))
    }

    // `Processing` protocol requires `Equatable` to identify cached images
    func ==(lhs: GaussianBlur, rhs: GaussianBlur) -> Bool {
        return lhs.radius == rhs.radius
    }
}

See Toucan plugin for some useful image transformations

Preheating Images

Preheating (prefetching) means loading images ahead of time in anticipation of its use. Nuke provides a Preheater class that does just that:

let preheater = Preheater()

// User enters the screen:
let requests = [Request(url: url1), Request(url: url2), ...]
preheater.startPreheating(for: requests)

// User leaves the screen:
preheater.stopPreheating(for: requests)

Automating Preheating

You can use Nuke in combination with Preheat library which automates preheating of content in UICollectionView and UITableView.

let preheater = Preheater()
let controller = Preheat.Controller(view: collectionView)
controller.handler = { addedIndexPaths, removedIndexPaths in
    preheater.startPreheating(for: requests(for: addedIndexPaths))
    preheater.stopPreheating(for: requests(for: removedIndexPaths))
}

See Performance Guide to see what else you can do to improve performance

Loading Images Directly

One of the Nuke's core classes is Loader. Its API and implementation is based on Promises. You can use it to load images directly.

Loader.shared.loadImage(with: url).completion {
    print("image \($0.value)")
}

Plugins

Alamofire Plugin

Allows you to replace networking layer with Alamofire. Combine the power of both frameworks!

Gifu Plugin

Gifu plugin allows you to load and display animated GIFs.

Toucan Plugin

Toucan plugin provides a simple API for processing images. It supports resizing, cropping, rounded rect masking and more.

FLAnimatedImage Plugin (Deprecated)

FLAnimatedImage plugin allows you to load and display animated GIFs with smooth scrolling performance and low memory footprint.

Design

Nuke is designed to support dependency injection. It provides a set of protocols - each with a single responsibility - which manage loading, decoding, processing, and caching images. You can easily create and inject your own implementations of those protocols:

Protocol Description
Loading Loads images
DataLoading Downloads data
DataCaching Stores data into disk cache
DataDecoding Converts data into image objects
Processing Image transformations
Caching Stores images into memory cache

Data Loading and Caching

Nuke has a basic built-in DataLoader class that implements DataLoading protocol. It uses Foundation.URLSession which is a part of the Foundation's URL Loading System. Another part of it is Foundation.URLCache which provides a composite in-memory and on-disk cache for data. By default it is initialized with a memory capacity of 0 MB (Nuke only stores decompressed images in memory) and a disk capacity of 200 MB.

See Image Caching Guide to learn more about URLCache, HTTP caching, and more

Most developers either have their own networking layer, or use some third-party framework. Nuke supports both of these workflows. You can integrate a custom networking layer by implementing DataLoading protocol.

See Alamofire Plugin that implements DataLoading protocol using Alamofire framework

Another useful protocol in Nuke is DataCaching. It is used by CachingDataLoader which wraps around DataLoading object to add a custom cache layer for image data. The main reason to use it is performance. While built-in Foundation.URLCache is a great option - it's available out of the box, it's hip to cache control and handles cache revalidation transparently - it might be slow and unpredictable at times.

Memory Cache

Nuke provides a fast in-memory Cache that implements Caching protocol. It stores processed images ready to be displayed. Cache uses LRU (least-recently used) replacement algorithm. By default it is initialized with a memory capacity of 20% of the available RAM. As a good citizen Cache automatically evicts images on memory warnings, and removes most of the images when application enters background.

Requirements

  • iOS 9.0 / watchOS 2.0 / macOS 10.11 / tvOS 9.0
  • Xcode 8
  • Swift 3

License

Nuke is available under the MIT license. See the LICENSE file for more info.