iOS多线程 - 下载及图片缓存

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线程可以理解为下载的通道，一个线程就是一个文件的下载通道，多线程也就是同时开起好几个下载通道.当服务器提供下载服务时，使用下载者是共享带宽的，在优先级相同的情况下，总服务器会对总下载线程进行平均分配。不难理解，如果你线程多的话，那下载的越快。现流行的下载软件都支持多线程。

下面我们通过代码来了解以下几个知识点：

  1. 多线程下载；
  2. 自定义 NSOperation ；
  3. NSCache 增删改查；
  4. NSFileManager 增删改查；
  5. 代理模式；
  6. 闭包反向传值；
  7. 扩展方法；
  8. Plist 文件解析；

首先我们给 String 类型添加扩展方法，获取字符串的MD5值：

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extension String {
    var md5 : String{
        let str = self.cStringUsingEncoding(NSUTF8StringEncoding)
        let strLen = CC_LONG(self.lengthOfBytesUsingEncoding(NSUTF8StringEncoding))
        let digestLen = Int(CC_MD5_DIGEST_LENGTH)
        let result = UnsafeMutablePointer<CUnsignedChar>.alloc(digestLen);
        CC_MD5(str!, strLen, result);
        let hash = NSMutableString();
        for i in 0 ..< digestLen {
            hash.appendFormat("%02x", result[i]);
        }
        result.destroy();
        return String(format: hash as String)
    }
}

下面我们来自定义一个 NSOperation ，新建一个继承自 NSOperation 的类，并声明以下属性：

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class DownloadOperation: NSOperation {
    var memCache: NSCache!
    var fileMgr: NSFileManager!
    var diskCachePath: String!
    var operations: [NSOperation] = []
    var getImageQueue: NSOperationQueue!
}

然后声明一个闭包：

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typealias Block = (UIImage) -> (Void)

最后声明一个协议，并创建两个代理方法：

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protocol DownloadDelegate {
    func userCache (operation: DownloadOperation, imageCache:NSCache)
    func cleanCache (operation: DownloadOperation, imageCache:NSCache)
}

下面我们重写自定义 NSOperation 的 init 方法，用来创建沙盒目录，实例 NSCache NSFileManager NSOperationQueue ：

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override init() {
    memCache = NSCache()
    fileMgr = NSFileManager()
    let paths = NSSearchPathForDirectoriesInDomains(NSSearchPathDirectory.DocumentDirectory,
                                                    NSSearchPathDomainMask.UserDomainMask,
                                                    true)
    self.diskCachePath = paths.first?.stringByAppendingString("/ImageCache")
    if !(NSFileManager.defaultManager().fileExistsAtPath(self.diskCachePath!)) {
        try! NSFileManager.defaultManager().createDirectoryAtPath(self.diskCachePath!,
                                                                  withIntermediateDirectories: true,
                                                                  attributes: nil)
    }
    getImageQueue = NSOperationQueue()
}

下面是闭包反向传值的第一步，初始化闭包：

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func ininWithblock(block: Block) {
    showImage = block
}

下面我们利用文件名获得要保存的路径：

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func diskPathForKey(key: String) -> String {
    return (diskCachePath?.stringByAppendingString("/\(key.md5)"))!
}

下面我们利用文件名判断这个文件在内存中是否存在：

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func cacheIsExist(key: String) -> Bool {
    let data = memCache.objectForKey(key)
    if data != nil {
        return true
    }
    else {
        return false
    }
}

下面我们利用文件名判断这个文件在磁盘中是否存在：

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func fileIsExist(key: String) -> Bool {
    return fileMgr.fileExistsAtPath(diskPathForKey(key))
}

下面我们实现利用文件名从内存中获取文件：

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func readFromeMem(key: String) -> UIImage {
    let image = memCache.objectForKey(key) as! UIImage
    return image
}

下面我们实现利用文件名从磁盘中获取文件：

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func readFromeDisk(key: String) -> UIImage {
    let  data = fileMgr.contentsAtPath(diskPathForKey(key))
    let image = UIImage(data: data!)
    return image!
}

下面我们实现利用链接下载文件：

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func download(key: String) -> UIImage {
    let url = NSURL(string: key)
    let data = NSData(contentsOfURL: url!)
    let image = UIImage(data: data!)
    return image!
}

下面实现将文件写入内存：

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func saveToMem(image: UIImage, key: String) {
    memCache.setObject(image, forKey: key)
}

下载实现将文件写入磁盘：

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func saveToDisk(image: UIImage, key: String) {
    let key = diskPathForKey(key)
    fileMgr.createFileAtPath(key,
                             contents: UIImageJPEGRepresentation(image, 1.0),
                             attributes: nil)
}

下面实现利用链接下载文件，并将下载的文件写入内存和磁盘：

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func saveToMemAndDisk(key: String, toDisk: Bool) {
    let image = download(key)
    saveToMem(image, key: key)
    if toDisk {
        saveToDisk(image, key: key)
    }
}

下面实现读取文件，如果内存中有就从内存读取，如果磁盘中有就从磁盘读取，并写入到内存，如果都没有，就下载并写入到内存和磁盘：

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func readImage(key: String) -> UIImage {
    if cacheIsExist(key) {
        let image = readFromeMem(key)
        return image
    }
    else if fileIsExist(key) {
        let image = readFromeDisk(key)
        saveToMem(image, key: key)
        return image
    }
    saveToMemAndDisk(key, toDisk: true)
    return readFromeMem(key)
}

下面实现利用存放链接的数组，批量下载文件，设置下载线程的最大值并使用 block 执行 ViewController 预设的方法：

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func getImage(keys: [String], max: Int) {
    for key in keys {
        let operation = NSBlockOperation(block: {
            let image = self.readImage(key)
            self.showImage!(image)
        })
        operations.append(operation)
    }
    getImageQueue.maxConcurrentOperationCount = max
    getImageQueue.addOperations(operations, waitUntilFinished: true)
}

下面实现利用文件名删除文件：

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func deleteFile(key: String) {
    if fileMgr.isDeletableFileAtPath(key) {
        print("删除成功")
    }

下面实现调用代理的两个方法：

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func showImg() {
    if (self.delegete != nil) && (self.delegete?.userCache != nil) {
        self.delegete?.userCache(self, imageCache: self.memCache)
    }
}
func deleteImg() {
    if (self.delegete != nil) && (self.delegete?.cleanCache != nil) {
        self.delegete?.cleanCache(self, imageCache: self.memCache)
    }
}

下面我们回到 ViewController 中，声明以下几个属性：

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class ViewController: UIViewController {
    var keys: NSArray!
    var imgView: UIImageView!
    var downloadBtn: UIButton?
    var cleanBtn: UIButton?
    var operation: DownloadOperation!
}

下面我们创建 block 要执行的方法：

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func showImage(image: UIImage) {
    self.imgView = UIImageView(frame: self.view.bounds)
    self.view.addSubview(self.imgView!)
    self.imgView.image = image
    print("block 加载图片")
}

下面我们解析 Plist 文件为数组，并将包含下载链接的数组传给自定义 NSOperation 的获取文件方法：

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func downloadForKeys(max: Int) {
    let imgPaths = NSBundle.mainBundle().pathForResource("ImageLinks", ofType: "plist")
    let imgUrls = NSURL(fileURLWithPath: imgPaths!)
    self.keys = NSArray(contentsOfURL: imgUrls)!
    operation.getImage(keys as! [String], max: max)
}

下面我们给 ViewController 添加两个 Button ：

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func addButton() {
    let width = self.view.bounds.size.width
    let height = self.view.bounds.size.height
    self.downloadBtn = UIButton(type: .Custom)
    let downloadBtnframe = CGRectMake(20, height-60, 80, 40)
    self.downloadBtn?.frame = downloadBtnframe
    self.downloadBtn?.backgroundColor = UIColor.lightGrayColor()
    self.downloadBtn?.titleLabel?.font = UIFont.systemFontOfSize(18)
    self.downloadBtn?.setTitle("下载", forState: .Normal)
    self.cleanBtn = UIButton(type: .Custom)
    let cleanBtnframe = CGRectMake(width-80-20, height-60, 80, 40)
    self.cleanBtn?.frame = cleanBtnframe
    self.cleanBtn?.backgroundColor = UIColor.lightGrayColor()
    self.cleanBtn?.titleLabel?.font = UIFont.systemFontOfSize(18)
    self.cleanBtn?.setTitle("清除", forState: .Normal)
    self.downloadBtn?.addTarget(self,
                                action: #selector(ViewController.downloadBtnClicked),
                                forControlEvents: .TouchUpInside)
    self.cleanBtn?.addTarget(self,
                                action: #selector(ViewController.cleanBtnClicked),
                                forControlEvents: .TouchUpInside)
    self.view.addSubview(self.downloadBtn!)
    self.view.addSubview(self.cleanBtn!)
}

下面我们实现 Button 的响应事件方法：

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func downloadBtnClicked() {
    operation.showImg()
    addButton()
}
func cleanBtnClicked() {
    operation.deleteImg()
}

下面我们实现代理方法：

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func userCache(operation: DownloadOperation, imageCache: NSCache) {
    imgView.removeFromSuperview()
    let width = self.view.bounds.size.width
    let imgHeight = self.view.bounds.size.height / CGFloat(Float(keys.count))
    for i in 0 ..< keys.count {
        let frame = CGRectMake(0, CGFloat(i) * imgHeight, width, imgHeight)
        let imageView = UIImageView(frame: frame)
        let key = keys[i] as! String
        let image = operation.readImage(key)
        imageView.image = image
        imageView.contentMode = .ScaleToFill
        self.view.addSubview(imageView)
    }
}
func cleanCache (operation: DownloadOperation, imageCache:NSCache) {
    imageCache.removeAllObjects()
    for subView in self.view.subviews {
        subView.removeFromSuperview()
    }
    for key in keys {
        let temKey = operation.diskPathForKey(key as! String)
        operation.deleteFile(temKey)
    }
    addButton()
}

最后我们引入代理协议，实例化自定义的 ，实例化代理对象，实例化 block，以上几个功能点就完成了：

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class ViewController: UIViewController, DownloadDelegate {
    var keys: NSArray!
    var imgView: UIImageView!
    var downloadBtn: UIButton?
    var cleanBtn: UIButton?
    var operation: DownloadOperation!
    override func viewDidLoad() {
        super.viewDidLoad()
        operation = DownloadOperation()
        operation.ininWithblock(showImage)
        operation.delegete = self
        downloadForKeys(3)
        addButton()
    }
}

完整代码如下：

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extension String {
    var md5 : String{
        let str = self.cStringUsingEncoding(NSUTF8StringEncoding)
        let strLen = CC_LONG(self.lengthOfBytesUsingEncoding(NSUTF8StringEncoding))
        let digestLen = Int(CC_MD5_DIGEST_LENGTH)
        let result = UnsafeMutablePointer<CUnsignedChar>.alloc(digestLen);
        CC_MD5(str!, strLen, result);
        let hash = NSMutableString();
        for i in 0 ..< digestLen {
            hash.appendFormat("%02x", result[i]);
        }
        result.destroy();
        return String(format: hash as String)
    }
}
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typealias Block = (UIImage) -> (Void)
protocol DownloadDelegate {
    func userCache (operation: DownloadOperation, imageCache:NSCache)
    func cleanCache (operation: DownloadOperation, imageCache:NSCache)
}
class DownloadOperation: NSOperation {
    var memCache: NSCache!
    var fileMgr: NSFileManager!
    var diskCachePath: String!
    var operations: [NSOperation] = []
    var getImageQueue: NSOperationQueue!
    var showImage: Block?
    var delegete:DownloadDelegate?
    override init() {
        memCache = NSCache()
        fileMgr = NSFileManager()
        let paths = NSSearchPathForDirectoriesInDomains(NSSearchPathDirectory.DocumentDirectory,
                                                        NSSearchPathDomainMask.UserDomainMask,
                                                        true)
        self.diskCachePath = paths.first?.stringByAppendingString("/ImageCache")
        if !(NSFileManager.defaultManager().fileExistsAtPath(self.diskCachePath!)) {
            try! NSFileManager.defaultManager().createDirectoryAtPath(self.diskCachePath!,
                                                                      withIntermediateDirectories: true,
                                                                      attributes: nil)
        }
        getImageQueue = NSOperationQueue()
    }
    func ininWithblock(block: Block) {
        showImage = block
    }
    func diskPathForKey(key: String) -> String {
        return (diskCachePath?.stringByAppendingString("/\(key.md5)"))!
    }
    func fileIsExist(key: String) -> Bool {
        return fileMgr.fileExistsAtPath(diskPathForKey(key))
    }
    func cacheIsExist(key: String) -> Bool {
        let data = memCache.objectForKey(key)
        if data != nil {
            return true
        }
        else {
            return false
        }
    }
    func readFromeMem(key: String) -> UIImage {
        let image = memCache.objectForKey(key) as! UIImage
        print("内存读取")
        return image
    }
    func readFromeDisk(key: String) -> UIImage {
        let  data = fileMgr.contentsAtPath(diskPathForKey(key))
        let image = UIImage(data: data!)
        print("文件读取")
        return image!
    }
    func deleteFile(key: String) {
        if fileMgr.isDeletableFileAtPath(key) {
            print("删除成功")
        }
    }
    func download(key: String) -> UIImage {
        let url = NSURL(string: key)
        let data = NSData(contentsOfURL: url!)
        let image = UIImage(data: data!)
        print("下载")
        return image!
    }
    func saveToMemAndDisk(key: String, toDisk: Bool) {
        let image = download(key)
        saveToMem(image, key: key)
        if toDisk {
            saveToDisk(image, key: key)
        }
    }
    func saveToMem(image: UIImage, key: String) {
        memCache.setObject(image, forKey: key)
        print("写入内存")
    }
    func saveToDisk(image: UIImage, key: String) {
        let key = diskPathForKey(key)
        fileMgr.createFileAtPath(key,
                                 contents: UIImageJPEGRepresentation(image, 1.0),
                                 attributes: nil)
        print("写入文件")
    }
    func readImage(key: String) -> UIImage {
        if cacheIsExist(key) {
            let image = readFromeMem(key)
            return image
        }
        else if fileIsExist(key) {
            let image = readFromeDisk(key)
            saveToMem(image, key: key)
            return image
        }
        saveToMemAndDisk(key, toDisk: true)
        return readFromeMem(key)
    }
    func getImage(keys: [String], max: Int) {
        for key in keys {
            let operation = NSBlockOperation(block: {
                let image = self.readImage(key)
                self.showImage!(image)
            })
            operations.append(operation)
        }
        getImageQueue.maxConcurrentOperationCount = max
        getImageQueue.addOperations(operations, waitUntilFinished: true)
    }
    func showImg() {
        if (self.delegete != nil) && (self.delegete?.userCache != nil) {
            self.delegete?.userCache(self, imageCache: self.memCache)
        }
    }
    func deleteImg() {
        if (self.delegete != nil) && (self.delegete?.cleanCache != nil) {
            self.delegete?.cleanCache(self, imageCache: self.memCache)
        }
    }
}
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class ViewController: UIViewController, DownloadDelegate {
    var keys: NSArray!
    var imgView: UIImageView!
    var downloadBtn: UIButton?
    var cleanBtn: UIButton?
    var operation: DownloadOperation!
    override func viewDidLoad() {
        super.viewDidLoad()
        operation = DownloadOperation()
        operation.ininWithblock(showImage)
        operation.delegete = self
        downloadForKeys(3)
        addButton()
    }
    func downloadForKeys(max: Int) {
        let imgPaths = NSBundle.mainBundle().pathForResource("ImageLinks", ofType: "plist")
        let imgUrls = NSURL(fileURLWithPath: imgPaths!)
        self.keys = NSArray(contentsOfURL: imgUrls)!
        operation.getImage(keys as! [String], max: max)
    }
    func showImage(image: UIImage) {
        self.imgView = UIImageView(frame: self.view.bounds)
        self.view.addSubview(self.imgView!)
        self.imgView.image = image
        print("block 加载图片")
    }
    func addButton() {
        let width = self.view.bounds.size.width
        let height = self.view.bounds.size.height
        self.downloadBtn = UIButton(type: .Custom)
        let downloadBtnframe = CGRectMake(20, height-60, 80, 40)
        self.downloadBtn?.frame = downloadBtnframe
        self.downloadBtn?.backgroundColor = UIColor.lightGrayColor()
        self.downloadBtn?.titleLabel?.font = UIFont.systemFontOfSize(18)
        self.downloadBtn?.setTitle("下载", forState: .Normal)
        self.cleanBtn = UIButton(type: .Custom)
        let cleanBtnframe = CGRectMake(width-80-20, height-60, 80, 40)
        self.cleanBtn?.frame = cleanBtnframe
        self.cleanBtn?.backgroundColor = UIColor.lightGrayColor()
        self.cleanBtn?.titleLabel?.font = UIFont.systemFontOfSize(18)
        self.cleanBtn?.setTitle("清除", forState: .Normal)
        self.downloadBtn?.addTarget(self,
                                    action: #selector(ViewController.downloadBtnClicked),
                                    forControlEvents: .TouchUpInside)
        self.cleanBtn?.addTarget(self,
                                    action: #selector(ViewController.cleanBtnClicked),
                                    forControlEvents: .TouchUpInside)
        self.view.addSubview(self.downloadBtn!)
        self.view.addSubview(self.cleanBtn!)
    }
    func userCache(operation: DownloadOperation, imageCache: NSCache) {
        imgView.removeFromSuperview()
        let width = self.view.bounds.size.width
        let imgHeight = self.view.bounds.size.height / CGFloat(Float(keys.count))
        for i in 0 ..< keys.count {
            let frame = CGRectMake(0, CGFloat(i) * imgHeight, width, imgHeight)
            let imageView = UIImageView(frame: frame)
            let key = keys[i] as! String
            let image = operation.readImage(key)
            imageView.image = image
            imageView.contentMode = .ScaleToFill
            self.view.addSubview(imageView)
        }
    }
    func cleanCache (operation: DownloadOperation, imageCache:NSCache) {
        imageCache.removeAllObjects()
        for subView in self.view.subviews {
            subView.removeFromSuperview()
        }
        for key in keys {
            let temKey = operation.diskPathForKey(key as! String)
            operation.deleteFile(temKey)
        }
        addButton()
    }
    func downloadBtnClicked() {
        operation.showImg()
        addButton()
    }
    func cleanBtnClicked() {
        operation.deleteImg()
    }
}