ImageDownloader

public class ImageDownloader

The ImageDownloader class is responsible for downloading images in parallel on a prioritized queue. Incoming downloads are added to the front or back of the queue depending on the download prioritization. Each downloaded image is cached in the underlying NSURLCache as well as the in-memory image cache that supports image filters. By default, any download request with a cached image equivalent in the image cache will automatically be served the cached image representation. Additional advanced features include supporting multiple image filters and completion handlers for a single request.

DownloadPrioritization
Defines the order prioritization of incoming download requests being inserted into the queue.
- fifo: All incoming downloads are added to the back of the queue.
- lifo: All incoming downloads are added to the front of the queue.
Declaration
Swift

public enum DownloadPrioritization
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ProgressHandler
The progress handler closure called periodically during an image download.
Declaration
Swift

public typealias ProgressHandler = DataRequest.ProgressHandler
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CompletionHandler
The completion handler closure used when an image download completes.
Declaration
Swift

public typealias CompletionHandler = (DataResponse<Image>) -> Void
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Properties

imageCache
The image cache used to store all downloaded images in.
Declaration
Swift

public let imageCache: ImageRequestCache?
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credential
The credential used for authenticating each download request.
Declaration
Swift

public private(set) var credential: URLCredential?
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sessionManager
The underlying Alamofire Manager instance used to handle all download requests.
Declaration
Swift

public let sessionManager: SessionManager
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Initialization

default
The default instance of ImageDownloader initialized with default values.
Declaration
Swift

public static let `default` = ImageDownloader()
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defaultURLSessionConfiguration()
Creates a default URLSessionConfiguration with common usage parameter values.
Declaration
Swift

public class func defaultURLSessionConfiguration() -> URLSessionConfiguration
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defaultURLCache()
Creates a default URLCache with common usage parameter values.
Declaration
Swift

public class func defaultURLCache() -> URLCache
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                    init(configuration:downloadPrioritization:maximumActiveDownloads:imageCache:)

Initializes the ImageDownloader instance with the given configuration, download prioritization, maximum active download count and image cache.

Declaration

Swift

public init(
        configuration: URLSessionConfiguration = ImageDownloader.defaultURLSessionConfiguration(),
        downloadPrioritization: DownloadPrioritization = .fifo,
        maximumActiveDownloads: Int = 4,
        imageCache: ImageRequestCache? = AutoPurgingImageCache())

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                    init(sessionManager:downloadPrioritization:maximumActiveDownloads:imageCache:)

Initializes the ImageDownloader instance with the given session manager, download prioritization, maximum active download count and image cache.

Declaration

Swift

public init(
        sessionManager: SessionManager,
        downloadPrioritization: DownloadPrioritization = .fifo,
        maximumActiveDownloads: Int = 4,
        imageCache: ImageRequestCache? = AutoPurgingImageCache())

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Authentication


                    
                    
                    addAuthentication(user:password:persistence:)

Associates an HTTP Basic Auth credential with all future download requests.

Declaration

Swift

public func addAuthentication(
        user: String,
        password: String,
        persistence: URLCredential.Persistence = .forSession)

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addAuthentication(usingCredential:)
Associates the specified credential with all future download requests.
Declaration
Swift

public func addAuthentication(usingCredential credential: URLCredential)
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Download

download(_:receiptID:filter:progress:progressQueue:completion:)
Creates a download request using the internal Alamofire SessionManager instance for the specified URL request.

If the same download request is already in the queue or currently being downloaded, the filter and completion handler are appended to the already existing request. Once the request completes, all filters and completion handlers attached to the request are executed in the order they were added. Additionally, any filters attached to the request with the same identifiers are only executed once. The resulting image is then passed into each completion handler paired with the filter.

You should not attempt to directly cancel the request inside the request receipt since other callers may be relying on the completion of that request. Instead, you should call cancelRequestForRequestReceipt with the returned request receipt to allow the ImageDownloader to optimize the cancellation on behalf of all active callers.
Declaration
Swift

public func download( _ urlRequest: URLRequestConvertible, receiptID: String = UUID().uuidString, filter: ImageFilter? = nil, progress: ProgressHandler? = nil, progressQueue: DispatchQueue = DispatchQueue.main, completion: CompletionHandler?) -> RequestReceipt?
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download(_:filter:progress:progressQueue:completion:)
Creates a download request using the internal Alamofire SessionManager instance for each specified URL request.

For each request, if the same download request is already in the queue or currently being downloaded, the filter and completion handler are appended to the already existing request. Once the request completes, all filters and completion handlers attached to the request are executed in the order they were added. Additionally, any filters attached to the request with the same identifiers are only executed once. The resulting image is then passed into each completion handler paired with the filter.

You should not attempt to directly cancel any of the requests inside the request receipts array since other callers may be relying on the completion of that request. Instead, you should call cancelRequestForRequestReceipt with the returned request receipt to allow the ImageDownloader to optimize the cancellation on behalf of all active callers.
Declaration
Swift

public func download( _ urlRequests: [URLRequestConvertible], filter: ImageFilter? = nil, progress: ProgressHandler? = nil, progressQueue: DispatchQueue = DispatchQueue.main, completion: CompletionHandler? = nil) -> [RequestReceipt]
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cancelRequest(with:)
Cancels the request in the receipt by removing the response handler and cancelling the request if necessary.

If the request is pending in the queue, it will be cancelled if no other response handlers are registered with the request. If the request is currently executing or is already completed, the response handler is removed and will not be called.
Declaration
Swift

public func cancelRequest(with requestReceipt: RequestReceipt)
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