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Merge pull request onevcat#249 from krider2010/master
Provide a simple prefetcher implementation.
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| // | ||
| // ImagePrefetcher.swift | ||
| // Kingfisher | ||
| // | ||
| // Created by Claire Knight <[email protected]> on 24/02/2016 | ||
| // | ||
| // Copyright (c) 2016 Wei Wang <[email protected]> | ||
| // | ||
| // Permission is hereby granted, free of charge, to any person obtaining a copy | ||
| // of this software and associated documentation files (the "Software"), to deal | ||
| // in the Software without restriction, including without limitation the rights | ||
| // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell | ||
| // copies of the Software, and to permit persons to whom the Software is | ||
| // furnished to do so, subject to the following conditions: | ||
| // | ||
| // The above copyright notice and this permission notice shall be included in | ||
| // all copies or substantial portions of the Software. | ||
| // | ||
| // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR | ||
| // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, | ||
| // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE | ||
| // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER | ||
| // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, | ||
| // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN | ||
| // THE SOFTWARE. | ||
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| #if os(OSX) | ||
| import AppKit | ||
| #else | ||
| import UIKit | ||
| #endif | ||
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| /// Progress update block of prefetcher. | ||
| public typealias PrefetchProgressBlock = ((completedURLs: Int, allURLs: Int) -> ()) | ||
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| /// Completion block of prefetcher. | ||
| public typealias PrefetchCompletionBlock = ((cancelled: Bool, completedURLs: Int, skippedURLs: Int) -> ()) | ||
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| private let defaultPrefetcherInstance = ImagePrefetcher() | ||
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| /// `ImagePrefetcher` represents a downloading manager for requesting many images via URLs and caching them. | ||
| public class ImagePrefetcher: NSObject { | ||
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| private var prefetchURLs: [NSURL]? | ||
| private var skippedCount = 0 | ||
| private var requestedCount = 0 | ||
| private var finishedCount = 0 | ||
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| private var cancelCompletionHandlerCalled = false | ||
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| /// The default manager to use for downloads. | ||
| public lazy var manager: KingfisherManager = KingfisherManager.sharedManager | ||
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| /// The default prefetcher. | ||
| public class var defaultPrefetcher: ImagePrefetcher { | ||
| return defaultPrefetcherInstance | ||
| } | ||
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| /// The maximum concurrent downloads to use when prefetching images. Default is 5. | ||
| public var maxConcurrentDownloads = 5 | ||
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| /** | ||
| Download the images from `urls` and cache them. This can be useful for background downloading | ||
| of assets that are required for later use in an app. This code will not try and update any UI | ||
| with the results of the process, but calls the handlers with the number cached etc. Failed | ||
| images are just skipped. | ||
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| Warning: This will cancel any existing prefetch operation in progress! Use `isPrefetching() to | ||
| control this in your own code as you see fit. | ||
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| - parameter urls: The list of URLs to prefetch | ||
| - parameter progressBlock: Block to be called when progress updates. Completed and total | ||
| counts are provided. Completed does not imply success. | ||
| - parameter completionHandler: Block to be called when prefetching is complete. Completed is all | ||
| those made, and skipped is the number of failed ones. | ||
| */ | ||
| public func prefetchURLs(urls: [NSURL], progressBlock: PrefetchProgressBlock?, completionHandler: PrefetchCompletionBlock?) { | ||
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| // Clear out any existing prefetch operation first | ||
| cancelPrefetching() | ||
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| cancelCompletionHandlerCalled = false | ||
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| prefetchURLs = urls | ||
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| guard urls.count > 0 else { | ||
| CompletionHandler?() | ||
| return | ||
| } | ||
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| for i in (0..<urls.count) where i < maxConcurrentDownloads && requestedCount < urls.count { | ||
| startPrefetching(i, progressBlock: progressBlock, completionHandler: completionHandler) | ||
| } | ||
| } | ||
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| /** | ||
| This cancels any existing prefetching activity that might be occuring. It does not stop any currently | ||
| running cache operation, but prevents any further ones being started and terminates the looping. For | ||
| surety, be sure that the completion block on the prefetch is called after calling this if you expect | ||
| an operation to be running. | ||
| */ | ||
| func cancelPrefetching() { | ||
| prefetchURLs = .None | ||
| skippedCount = 0 | ||
| requestedCount = 0 | ||
| finishedCount = 0 | ||
| } | ||
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| /** | ||
| Checks to see if this prefetcher is already prefetching any images. | ||
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| - returns: True if there are images still to be prefetched, false otherwise. | ||
| */ | ||
| func isPrefetching() -> Bool { | ||
| guard let urls = prefetchURLs else { return false } | ||
| return urls.count > 0 | ||
| } | ||
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| internal func startPrefetching(index: Int, progressBlock: PrefetchProgressBlock?, completionHandler: PrefetchCompletionBlock?) { | ||
| guard let urls = prefetchURLs where index < (urls.count ?? 0) else { return } | ||
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| requestedCount++ | ||
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| let task = RetrieveImageTask() | ||
| let resource = Resource(downloadURL: urls[index]) | ||
| let total = urls.count | ||
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| manager.downloadAndCacheImageWithURL(resource.downloadURL, forKey: resource.cacheKey, retrieveImageTask: task, progressBlock: nil, completionHandler: { image, error, cacheType, imageURL in | ||
| self.finishedCount++ | ||
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| if image == .None { | ||
| self.skippedCount++ | ||
| } | ||
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| progressBlock?(completedURLs: self.finishedCount, allURLs: total) | ||
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| // Reference the prefetchURLs rather than urls in case the request has been cancelled | ||
| if (self.prefetchURLs?.count ?? 0) > self.requestedCount { | ||
| self.startPrefetching(self.requestedCount, progressBlock: progressBlock, completionHandler: completionHandler) | ||
| } else if self.finishedCount == self.requestedCount { | ||
| self.prefetchURLs?.removeAll() | ||
| completionHandler?(cancelled: false, completedURLs: self.finishedCount, skippedURLs: self.skippedCount) | ||
| } else if (self.prefetchURLs == nil || self.prefetchURLs!.count == 0) && !self.cancelCompletionHandlerCalled { | ||
| self.cancelCompletionHandlerCalled = true | ||
| completionHandler?(cancelled: true, completedURLs: self.finishedCount, skippedURLs: self.skippedCount) | ||
| } | ||
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| }, options: nil) | ||
| } | ||
| } |
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