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AlamofireImage

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AlamofireImage is an image component library for Alamofire.

Features

Requirements

Migration Guides

Dependencies

Communication

Installation

CocoaPods

CocoaPods is a dependency manager for Cocoa projects. For usage and installation instructions, visit their website. To integrate AlamofireImage into your Xcode project using CocoaPods, specify it in your Podfile:

pod 'AlamofireImage', '~> 4.3'

Carthage

Carthage is a decentralized dependency manager that builds your dependencies and provides you with binary frameworks. To integrate AlamofireImage into your Xcode project using Carthage, specify it in your Cartfile:

github "Alamofire/AlamofireImage" ~> 4.3

Swift Package Manager

The Swift Package Manager is a tool for automating the distribution of Swift code and is integrated into the swift compiler. It is in early development, but AlamofireImage does support its use on supported platforms.

Once you have your Swift package set up, adding AlamofireImage as a dependency is as easy as adding it to the dependencies value of your Package.swift.

dependencies: [
    .package(url: "https://github.com/Alamofire/AlamofireImage.git", .upToNextMajor(from: "4.3.0"))
]

Manually

If you prefer not to use either of the aforementioned dependency managers, you can integrate AlamofireImage into your project manually.

Embedded Framework

$ git init

$ git submodule add https://github.com/Alamofire/AlamofireImage.git

Usage

Image Response Serializers

import Alamofire
import AlamofireImage

AF.request("https://httpbin.org/image/png").responseImage { response in
  debugPrint(response)

  print(response.request)
  print(response.response)
  debugPrint(response.result)

  if case .success(let image) = response.result {
    print("image downloaded: \(image)")
  }
}

The AlamofireImage response image serializers support a wide range of image types including:

If the image you are attempting to download is an invalid MIME type not in the list, you can add custom acceptable content types using the addAcceptableImageContentTypes extension on the DataRequest type.

UIImage Extensions

There are several UIImage extensions designed to make the common image manipulation operations as simple as possible.

Inflation

let url = Bundle.main.url(forResource: "unicorn", withExtension: "png")!
let data = try! Data(contentsOf: url)
let image = UIImage(data: data, scale: UIScreen.main.scale)!

image.af.inflate()

Inflating compressed image formats (such as PNG or JPEG) in a background queue can significantly improve drawing performance on the main thread.

Scaling

let image = UIImage(named: "unicorn")!
let size = CGSize(width: 100.0, height: 100.0)

// Scale image to size disregarding aspect ratio
let scaledImage = image.af.imageScaled(to: size)

// Scale image to fit within specified size while maintaining aspect ratio
let aspectScaledToFitImage = image.af.imageAspectScaled(toFit: size)

// Scale image to fill specified size while maintaining aspect ratio
let aspectScaledToFillImage = image.af.imageAspectScaled(toFill: size)

Rounded Corners

let image = UIImage(named: "unicorn")!
let radius: CGFloat = 20.0

let roundedImage = image.af.imageRounded(withCornerRadius: radius)
let circularImage = image.af.imageRoundedIntoCircle()

Core Image Filters

let image = UIImage(named: "unicorn")!

let sepiaImage = image.af.imageFiltered(withCoreImageFilter: "CISepiaTone")

let blurredImage = image.af.imageFiltered(
    withCoreImageFilter: "CIGaussianBlur",
    parameters: ["inputRadius": 25]
)

Image Filters

The ImageFilter protocol was designed to make it easy to apply a filter operation and cache the result after an image finished downloading. It defines two properties to facilitate this functionality.

public protocol ImageFilter {
    var filter: Image -> Image { get }
    var identifier: String { get }
}

The filter closure contains the operation used to create a modified version of the specified image. The identifier property is a string used to uniquely identify the filter operation. This is useful when adding filtered versions of an image to a cache. All identifier properties inside AlamofireImage are implemented using protocol extensions.

Single Pass

The single pass image filters only perform a single operation on the specified image.

let image = UIImage(named: "unicorn")!
let imageFilter = RoundedCornersFilter(radius: 10.0)

let roundedImage = imageFilter.filter(image)

The current list of single pass image filters includes:

Each image filter is built ontop of the UIImage extensions.

Multi-Pass

The multi-pass image filters perform multiple operations on the specified image.

let image = UIImage(named: "avatar")!
let size = CGSize(width: 100.0, height: 100.0)
let imageFilter = AspectScaledToFillSizeCircleFilter(size: size)

let avatarImage = imageFilter.filter(image)

The current list of multi-pass image filters includes:

Image Cache

Image caching can become complicated when it comes to network images. URLCache is quite powerful and does a great job reasoning through the various cache policies and Cache-Control headers. However, it is not equipped to handle caching multiple modified versions of those images.

For example, let's say you need to download an album of images. Your app needs to display both the thumbnail version as well as the full size version at various times. Due to performance issues, you want to scale down the thumbnails to a reasonable size before rendering them on-screen. You also need to apply a global CoreImage filter to the full size images when displayed. While URLCache can easily handle storing the original downloaded image, it cannot store these different variants. What you really need is another caching layer designed to handle these different variants.

let imageCache = AutoPurgingImageCache(
    memoryCapacity: 100_000_000,
    preferredMemoryUsageAfterPurge: 60_000_000
)

The AutoPurgingImageCache in AlamofireImage fills the role of that additional caching layer. It is an in-memory image cache used to store images up to a given memory capacity. When the memory capacity is reached, the image cache is sorted by last access date, then the oldest image is continuously purged until the preferred memory usage after purge is met. Each time an image is accessed through the cache, the internal access date of the image is updated.

Add / Remove / Fetch Images

Interacting with the ImageCache protocol APIs is very straightforward.

let imageCache = AutoPurgingImageCache()
let avatarImage = UIImage(data: data)!

// Add
imageCache.add(avatarImage, withIdentifier: "avatar")

// Fetch
let cachedAvatar = imageCache.image(withIdentifier: "avatar")

// Remove
imageCache.removeImage(withIdentifier: "avatar")

URL Requests

The ImageRequestCache protocol extends the ImageCache protocol by adding support for URLRequest caching. This allows a URLRequest and an additional identifier to generate the unique identifier for the image in the cache.

let imageCache = AutoPurgingImageCache()

let urlRequest = URLRequest(url: URL(string: "https://httpbin.org/image/png")!)
let avatarImage = UIImage(named: "avatar")!.af.imageRoundedIntoCircle()

// Add
imageCache.add(avatarImage, for: urlRequest, withIdentifier: "circle")

// Fetch
let cachedAvatarImage = imageCache.image(for: urlRequest, withIdentifier: "circle")

// Remove
imageCache.removeImage(for: urlRequest, withIdentifier: "circle")

Auto-Purging

Each time an image is fetched from the cache, the cache internally updates the last access date for that image.

let avatar = imageCache.image(withIdentifier: "avatar")
let circularAvatar = imageCache.image(for: urlRequest, withIdentifier: "circle")

By updating the last access date for each image, the image cache can make more informed decisions about which images to purge when the memory capacity is reached. The AutoPurgingImageCache automatically evicts images from the cache in order from oldest last access date to newest until the memory capacity drops below the preferredMemoryCapacityAfterPurge.

It is important to set reasonable default values for the memoryCapacity and preferredMemoryCapacityAfterPurge when you are initializing your image cache. By default, the memoryCapacity equals 100 MB and the preferredMemoryCapacityAfterPurge equals 60 MB.

Memory Warnings

The AutoPurgingImageCache also listens for memory warnings from your application and will purge all images from the cache if a memory warning is observed.

Image Downloader

The ImageDownloader class is responsible for downloading images in parallel on a prioritized queue. It uses an internal Alamofire SessionManager instance to handle all the downloading and response image serialization. By default, the initialization of an ImageDownloader uses a default URLSessionConfiguration with the most common parameter values.

let imageDownloader = ImageDownloader(
    configuration: ImageDownloader.defaultURLSessionConfiguration(),
    downloadPrioritization: .fifo,
    maximumActiveDownloads: 4,
    imageCache: AutoPurgingImageCache()
)

If you need to customize the URLSessionConfiguration type or parameters, then simply provide your own rather than using the default.

Downloading an Image

let downloader = ImageDownloader()
let urlRequest = URLRequest(url: URL(string: "https://httpbin.org/image/jpeg")!)

downloader.download(urlRequest) { response in
    print(response.request)
    print(response.response)
    debugPrint(response.result)

    if case .success(let image) = response.result {
        print(image)
    }
}

Make sure to keep a strong reference to the ImageDownloader instance, otherwise the completion closure will not be called because the downloader reference will go out of scope before the completion closure can be called.

Applying an ImageFilter

let downloader = ImageDownloader()
let urlRequest = URLRequest(url: URL(string: "https://httpbin.org/image/jpeg")!)
let filter = AspectScaledToFillSizeCircleFilter(size: CGSize(width: 100.0, height: 100.0))

downloader.download(urlRequest, filter: filter) { response in
    print(response.request)
    print(response.response)
    debugPrint(response.result)

    if case .success(let image) = response.result {
        print(image)
    }
}

Authentication

If your images are behind HTTP Basic Auth, you can append the user:password: or the credential to the ImageDownloader instance. The credentials will be applied to all future download requests.

let downloader = ImageDownloader()
downloader.addAuthentication(user: "username", password: "password")

Download Prioritization

The ImageDownloader maintains an internal queue of pending download requests. Depending on your situation, you may want incoming downloads to be inserted at the front or the back of the queue. The DownloadPrioritization enumeration allows you to specify which behavior you would prefer.

public enum DownloadPrioritization {
    case fifo, lifo
}

The ImageDownloader is initialized with a .fifo queue by default.

Image Caching

The ImageDownloader uses a combination of an URLCache and AutoPurgingImageCache to create a very robust, high performance image caching system.

URLCache

The URLCache is used to cache all the original image content downloaded from the server. By default, it is initialized with a memory capacity of 20 MB and a disk capacity of 150 MB. This allows up to 150 MB of original image data to be stored on disk at any given time. While these defaults have been carefully set, it is very important to consider your application's needs and performance requirements and whether these values are right for you.

If you wish to disable this caching layer, create a custom URLSessionConfiguration with the urlCache property set to nil and use that configuration when initializing the ImageDownloader.

Image Cache

The ImageCache is used to cache all the potentially filtered image content after it has been downloaded from the server. This allows multiple variants of the same image to also be cached, rather than having to re-apply the image filters to the original image each time it is required. By default, an AutoPurgingImageCache is initialized with a memory capacity of 100 MB and a preferred memory usage after purge limit of 60 MB. This allows up to 100 MB of most recently accessed filtered image content to be stored in-memory at a given time.

Setting Ideal Capacity Limits

Determining the ideal the in-memory and on-disk capacity limits of the URLCache and AutoPurgingImageCache requires a bit of forethought. You must carefully consider your application's needs, and tailor the limits accordingly. By default, the combination of caches offers the following storage capacities:

If you do not use image filters, it is advised to set the memory capacity of the URLCache to zero. Otherwise, you will be storing the original image data in both the URLCache's in-memory store as well as the AlamofireImage in-memory store.

Duplicate Downloads

Sometimes application logic can end up attempting to download an image more than once before the initial download request is complete. Most often, this results in the image being downloaded more than once. AlamofireImage handles this case elegantly by merging the duplicate downloads. The image will only be downloaded once, yet both completion handlers will be called.

Image Filter Reuse

In addition to merging duplicate downloads, AlamofireImage can also merge duplicate image filters. If two image filters with the same identifier are attached to the same download, the image filter is only executed once and both completion handlers are called with the same resulting image. This can save large amounts of time and resources for computationally expensive filters such as ones leveraging CoreImage.

Request Receipts

Sometimes it is necessary to cancel an image download for various reasons. AlamofireImage can intelligently handle cancellation logic in the ImageDownloader by leveraging the RequestReceipt type along with the cancelRequestForRequestReceipt method. Each download request vends a RequestReceipt which can be later used to cancel the request.

By cancelling the request through the ImageDownloader using the RequestReceipt, AlamofireImage is able to determine how to best handle the cancellation. The cancelled download will always receive a cancellation error, while duplicate downloads are allowed to complete. If the download is already active, it is allowed to complete even though the completion handler will be called with a cancellation error. This greatly improves performance of table and collection views displaying large amounts of images.

It is NOT recommended to directly call cancel on the request in the RequestReceipt. Doing so can lead to issues such as duplicate downloads never being allowed to complete.

UIImageView Extension

The UIImage Extensions, Image Filters, Image Cache and Image Downloader were all designed to be flexible and standalone, yet also to provide the foundation of the UIImageView extension. Due to the powerful support of these classes, protocols and extensions, the UIImageView APIs are concise, easy to use and contain a large amount of functionality.

Setting Image with URL

Setting the image with a URL will asynchronously download the image and set it once the request is finished.

let imageView = UIImageView(frame: frame)
let url = URL(string: "https://httpbin.org/image/png")!

imageView.af.setImage(withURL: url)

If the image is cached locally, the image is set immediately.

Placeholder Images

By specifying a placeholder image, the image view uses the placeholder image until the remote image is downloaded.

let imageView = UIImageView(frame: frame)
let url = URL(string: "https://httpbin.org/image/png")!
let placeholderImage = UIImage(named: "placeholder")!

imageView.af.setImage(withURL: url, placeholderImage: placeholderImage)

If the remote image is cached locally, the placeholder image is never set.

Image Filters

If an image filter is specified, it is applied asynchronously after the remote image is downloaded. Once the filter execution is complete, the resulting image is set on the image view.

let imageView = UIImageView(frame: frame)

let url = URL(string: "https://httpbin.org/image/png")!
let placeholderImage = UIImage(named: "placeholder")!

let filter = AspectScaledToFillSizeWithRoundedCornersFilter(
    size: imageView.frame.size,
    radius: 20.0
)

imageView.af.setImage(
    withURL: url,
    placeholderImage: placeholderImage,
    filter: filter
)

If the remote image with the applied filter is cached locally, the image is set immediately.

Image Transitions

By default, there is no image transition animation when setting the image on the image view. If you wish to add a cross dissolve or flip-from-bottom animation, then specify an ImageTransition with the preferred duration.

let imageView = UIImageView(frame: frame)

let url = URL(string: "https://httpbin.org/image/png")!
let placeholderImage = UIImage(named: "placeholder")!

let filter = AspectScaledToFillSizeWithRoundedCornersFilter(
    size: imageView.frame.size,
    radius: 20.0
)

imageView.af.setImage(
    withURL: url,
    placeholderImage: placeholderImage,
    filter: filter,
    imageTransition: .crossDissolve(0.2)
)

If the remote image is cached locally, the image transition is ignored.

Image Downloader

The UIImageView extension is powered by the default ImageDownloader instance. To customize cache capacities, download priorities, request cache policies, timeout durations, etc., please refer to the Image Downloader documentation.

Authentication

If an image requires and authentication credential from the UIImageView extension, it can be provided as follows:

ImageDownloader.default.addAuthentication(user: "user", password: "password")

Credits

Alamofire is owned and maintained by the Alamofire Software Foundation. You can follow them on Twitter at @AlamofireSF for project updates and releases.

Security Disclosure

If you believe you have identified a security vulnerability with AlamofireImage, you should report it as soon as possible via email to security@alamofire.org. Please do not post it to a public issue tracker.

Donations

The ASF is looking to raise money to officially stay registered as a federal non-profit organization. Registering will allow us members to gain some legal protections and also allow us to put donations to use, tax free. Donating to the ASF will enable us to:

The community adoption of the ASF libraries has been amazing. We are greatly humbled by your enthusiasm around the projects, and want to continue to do everything we can to move the needle forward. With your continued support, the ASF will be able to improve its reach and also provide better legal safety for the core members. If you use any of our libraries for work, see if your employers would be interested in donating. Any amount you can donate today to help us reach our goal would be greatly appreciated.

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License

AlamofireImage is released under the MIT license. See LICENSE for details.