SDWebImage-SDWebImageManger

SDWebImage

下载图片的设置请求头参数：

在SDWebImageManager 管理器中设置请求头参数
在下载器中启用cookes

SDWebImageManager *sdmanger = [SDWebImageManager sharedManager];
    [sdmanger.imageDownloader setValue:@"true" forHTTPHeaderField:@"thumbnail"];
    
SDWebImageDownloader *downLoader = [SDWebImageDownloader sharedDownloader];
    [downLoader downloadImageWithURL:@"111" options:SDWebImageDownloaderHandleCookies progress:^(NSInteger receivedSize, NSInteger expectedSize) {
        
    } completed:^(UIImage *image, NSData *data, NSError *error, BOOL finished) {
        
    }];

UIImageView分类方法

// 内部实现还是和上边一样 。
    [imageView sd_setImageWithURL:@"" placeholderImage:@"" options:SDWebImageHandleCookies];

options

SDWebImageRetryFailed = 1 << 0, 默认情况下,如果一个url在下载的时候失败了,那么这个url会被加入黑名单并且library不会尝试再次下载,这个flag会阻止library把失败的url加入黑名单(简单来说如果选择了这个flag,那么即使某个url下载失败了,sdwebimage还是会尝试再次下载他.)
SDWebImageLowPriority = 1 << 1, 默认情况下,图片会在交互发生的时候下载(例如你滑动tableview的时候),这个flag会禁止这个特性,导致的结果就是在scrollview减速的时候才会开始下载(也就是你滑动的时候scrollview不下载,你手从屏幕上移走,scrollview开始减速的时候才会开始下载图片)可以增加UI的流畅度
SDWebImageCacheMemoryOnly = 1 << 2,禁止磁盘缓存
SDWebImageProgressiveDownload = 1 << 3,渐进显示实时的下载图片，默认是只显示完整下载后的图。
SDWebImageRefreshCached = 1 << 4,即使有缓存，也再次从远程请求图片。这个时候缓存由NSURLCache 管理。
SDWebImageContinueInBackground = 1 << 5,ios4以上，当app到后台，请求增加后台下载的时间。
SDWebImageHandleCookies = 1 << 6,下载时，允许使用cookes NSMutableURLRequest.HTTPShouldHandleCookies = YES;
SDWebImageAllowInvalidSSLCertificates = 1 << 7,启用允许不受信任的SSL证书。不推荐使用
SDWebImageHighPriority = 1 << 8, 默认情况下,image在装载的时候是按照他们在队列中的顺序装载的(就是先进先出).这个flag会把他们移动到队列的前端,并且立刻装载而不是等到当前队列装载的时候再装载.
SDWebImageDelayPlaceholder = 1 << 9,
SDWebImageTransformAnimatedImage = 1 << 10, 是否transform图片

UIImageView+WebCache的实现

执行的其实就是SDWebImageManager 。他会绑定一个下载器也就是SDWebImageDownloader和一个缓存SDImageCache.后面的大意应该是讲你可以直接使用一个其他上下文环境的SDWebImageManager,而不是仅仅限于一个UIView.

    SDWebImageManager *manager = [SDWebImageManager sharedManager];         
    [manager downloadImageWithURL:imageURL
                          options:0
                         progress:nil
                completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, BOOL finished, NSURL *imageURL) {
                    if (image) {
                        // do something with image
                    }];

SDWebImageManager中其它方法

主要作用是当缓存里没有发现某张图片的缓存时,是否选择下载这张图片(默认是yes),可以选择no,那么sdwebimage在缓存中没有找到这张图片的时候不会选择下载
```
  - (BOOL)imageManager:(SDWebImageManager *)imageManager shouldDownloadImageForURL:(NSURL *)imageURL;
```
在图片下载完成并且还没有加入磁盘缓存或者内存缓存的时候就transform这个图片.这个方法是在异步线程执行的,防治阻塞主线程.
```
  - (UIImage *)imageManager:(SDWebImageManager *)imageManager transformDownloadedImage:(UIImage *)image withURL:(NSURL *)imageURL;
```
这个cacheKeyFilter是干嘛的呢?很简单.1他是一个block.2.这个block的作用就是生成一个image的key.因为sdwebimage的缓存原理你可以当成是一个字典,每一个字典的value就是一张image,那么这个value对应的key是什么呢?就是cacheKeyFilter根据某个规则对这个图片的url做一些操作生成的.
```
  typedef NSString *(^SDWebImageCacheKeyFilterBlock)(NSURL *url);

      
  @property (nonatomic, copy) SDWebImageCacheKeyFilterBlock cacheKeyFilter;
```

[[SDWebImageManager sharedManager] setCacheKeyFilter:^(NSURL *url) {
   url = [[NSURL alloc] initWithScheme:url.scheme host:url.host path:url.path];
   return [url absoluteString];
}];

这个方法主要就是SDWebImage下载图片的方法了.
第一个参数是必须要的,就是image的url
第二个参数就是我们上面的Options,你可以定制化各种各样的操作.详情参上.
第三个参数是一个回调block,用于图片在下载过程中的回调.
第四个参数是一个下载完成的回调.会在图片下载完成后回调.
返回值是一个NSObject类,并且这个NSObject类是conforming一个协议这个协议叫做SDWebImageOperation,这个协议很简单,就是一个cancel掉operation的协议.

        -(id )downloadImageWithURL:(NSURL *)url
                                     options:(SDWebImageOptions)options
                                    progress:(SDWebImageDownloaderProgressBlock)progressBlock
                                   completed:(SDWebImageCompletionWithFinishedBlock)completedBlock;

取消掉当前所有的下载图片的operation
```
  - (void)cancelAll;
```

将图片存入cache的方法,类似于字典的setValue: forKey:

  - (void)saveImageToCache:(UIImage *)image forURL:(NSURL *)url;

check一下是否有一个或者多个operation正在执行(简单来说就是check是否有图片在下载)
```
  - (BOOL)isRunning;
```
检测一个image是否已经被缓存到磁盘(是否存且仅存在disk里).
```
  - (BOOL)diskImageExistsForURL:(NSURL *)url;
```
如果检测到图片已经被缓存,那么执行回调block.这个block会永远执行在主线程.也就是你可以在这个回调block里更新ui.（也就是用一个url 来获取缓存的图片，并且这个blcok是在主线程）
```
  - (void)cachedImageExistsForURL:(NSURL *)url
               completion:(SDWebImageCheckCacheCompletionBlock)completionBlock;
```
通过image的url返回image存在缓存里的key.为什么不直接把图片的url当做image的key来使用呢?而是非要对url做一些处理才能当做key.我的解释是,我也不太清楚.可能为了防止重复吧.
```
 - (NSString *)cacheKeyForURL:(NSURL *)url;
```

通过url建立一个operation用来下载图片.

- (id )downloadImageWithURL:(NSURL *)url
                                         options:(SDWebImageOptions)options
                                        progress:(SDWebImageDownloaderProgressBlock)progressBlock
                                       completed:(SDWebImageCompletionWithFinishedBlock)completedBlock {
    // Invoking this method without a completedBlock is pointless
    NSAssert(completedBlock != nil, @"If you mean to prefetch the image, use -[SDWebImagePrefetcher prefetchURLs] instead");
 
    // Very common mistake is to send the URL using NSString object instead of NSURL. For some strange reason, XCode won't
    // throw any warning for this type mismatch. Here we failsafe this error by allowing URLs to be passed as NSString.
    if ([url isKindOfClass:NSString.class]) {
        url = [NSURL URLWithString:(NSString *)url];
    }
 
    // Prevents app crashing on argument type error like sending NSNull instead of NSURL
    if (![url isKindOfClass:NSURL.class]) {
        url = nil;
    }
 
    __block SDWebImageCombinedOperation *operation = [SDWebImageCombinedOperation new];
    __weak SDWebImageCombinedOperation *weakOperation = operation;
 
    BOOL isFailedUrl = NO;
    // 创建一个互斥锁防止现在有别的线程修改failedURLs.
    // 判断这个url是否是fail过的.如果url failed过的那么isFailedUrl就是true
    @synchronized (self.failedURLs) {
        isFailedUrl = [self.failedURLs containsObject:url];
    }
    // 如果url不存在那么直接返回一个block,如果url存在.那么继续进行判断.
    // options与SDWebImageRetryFailed这个option进行按位与操作.判断用户的options里是否有retry这个option.
    // 如果用户的options里没有retry这个选项并且isFaileUrl 是true.那么就回调一个error的block.
    if (!url || (!(options & SDWebImageRetryFailed) && isFailedUrl)) {
        dispatch_main_sync_safe(^{
            NSError *error = [NSError errorWithDomain:NSURLErrorDomain code:NSURLErrorFileDoesNotExist userInfo:nil];
            completedBlock(nil, error, SDImageCacheTypeNone, YES, url);
        });
        return operation;
    }
 
    // 创建一个互斥锁防止现在有别的线程修改runningOperations.
    @synchronized (self.runningOperations) {
        [self.runningOperations addObject:operation];
    }
    NSString *key = [self cacheKeyForURL:url];
 
    // cacheOperation应该是一个用来下载图片并且缓存的operation
    operation.cacheOperation = [self.imageCache queryDiskCacheForKey:key done:^(UIImage *image, SDImageCacheType cacheType) {
        // 判断operation这时候有没有执行cancel操作,如果cancel掉了就把这个operation从我们的operation数组里remove掉然后return
        if (operation.isCancelled) {
            @synchronized (self.runningOperations) {
                [self.runningOperations removeObject:operation];
            }
 
            return;
        }
 
        if ((!image || options & SDWebImageRefreshCached) && (![self.delegate respondsToSelector:@selector(imageManager:shouldDownloadImageForURL:)] || [self.delegate imageManager:self shouldDownloadImageForURL:url])) {
            if (image && options & SDWebImageRefreshCached) {
                dispatch_main_sync_safe(^{
                    // If image was found in the cache bug SDWebImageRefreshCached is provided, notify about the cached image
                    // AND try to re-download it in order to let a chance to NSURLCache to refresh it from server.
                    completedBlock(image, nil, cacheType, YES, url);
                });
            }
 
            // download if no image or requested to refresh anyway, and download allowed by delegate
            // 下面都是判断我们的options里包含哪些SDWebImageOptions,然后给我们的downloaderOptions相应的添加对应的SDWebImageDownloaderOptions. downloaderOptions |= SDWebImageDownloaderLowPriority这种表达式的意思等同于
            // downloaderOptions = downloaderOptions | SDWebImageDownloaderLowPriority
            SDWebImageDownloaderOptions downloaderOptions = 0;
            if (options & SDWebImageLowPriority) downloaderOptions |= SDWebImageDownloaderLowPriority;
            if (options & SDWebImageProgressiveDownload) downloaderOptions |= SDWebImageDownloaderProgressiveDownload;
            if (options & SDWebImageRefreshCached) downloaderOptions |= SDWebImageDownloaderUseNSURLCache;
            if (options & SDWebImageContinueInBackground) downloaderOptions |= SDWebImageDownloaderContinueInBackground;
            if (options & SDWebImageHandleCookies) downloaderOptions |= SDWebImageDownloaderHandleCookies;
            if (options & SDWebImageAllowInvalidSSLCertificates) downloaderOptions |= SDWebImageDownloaderAllowInvalidSSLCertificates;
            if (options & SDWebImageHighPriority) downloaderOptions |= SDWebImageDownloaderHighPriority;
            if (image && options & SDWebImageRefreshCached) {
                // force progressive off if image already cached but forced refreshing
                downloaderOptions &= ~SDWebImageDownloaderProgressiveDownload;
                // ignore image read from NSURLCache if image if cached but force refreshing
                downloaderOptions |= SDWebImageDownloaderIgnoreCachedResponse;
            }
 
            // 调用imageDownloader去下载image并且返回执行这个request的download的operation
            id  subOperation = [self.imageDownloader downloadImageWithURL:url options:downloaderOptions progress:progressBlock completed:^(UIImage *downloadedImage, NSData *data, NSError *error, BOOL finished) {
                if (weakOperation.isCancelled) {
                    // Do nothing if the operation was cancelled
                    // See #699 for more details
                    // if we would call the completedBlock, there could be a race condition between this block and another completedBlock for the same object, so if this one is called second, we will overwrite the new data
                }
                else if (error) {
                    dispatch_main_sync_safe(^{
                        if (!weakOperation.isCancelled) {
                            completedBlock(nil, error, SDImageCacheTypeNone, finished, url);
                        }
                    });
 
                    if (error.code != NSURLErrorNotConnectedToInternet && error.code != NSURLErrorCancelled && error.code != NSURLErrorTimedOut) {
                        @synchronized (self.failedURLs) {
                            [self.failedURLs addObject:url];
                        }
                    }
                }
                else {
                    if ((options & SDWebImageRetryFailed)) {
                        @synchronized (self.failedURLs) {
                            [self.failedURLs removeObject:url];
                        }
                    }
 
                    BOOL cacheOnDisk = !(options & SDWebImageCacheMemoryOnly);
 
                    if (options & SDWebImageRefreshCached && image && !downloadedImage) {
                        // Image refresh hit the NSURLCache cache, do not call the completion block
                    }
                    else if (downloadedImage && (!downloadedImage.images || (options & SDWebImageTransformAnimatedImage)) && [self.delegate respondsToSelector:@selector(imageManager:transformDownloadedImage:withURL:)]) {
                        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
                            UIImage *transformedImage = [self.delegate imageManager:self transformDownloadedImage:downloadedImage withURL:url];
 
                            if (transformedImage && finished) {
                                BOOL imageWasTransformed = ![transformedImage isEqual:downloadedImage];
                                [self.imageCache storeImage:transformedImage recalculateFromImage:imageWasTransformed imageData:data forKey:key toDisk:cacheOnDisk];
                            }
 
                            dispatch_main_sync_safe(^{
                                if (!weakOperation.isCancelled) {
                                    completedBlock(transformedImage, nil, SDImageCacheTypeNone, finished, url);
                                }
                            });
                        });
                    }
                    else {
                        if (downloadedImage && finished) {
                            [self.imageCache storeImage:downloadedImage recalculateFromImage:NO imageData:data forKey:key toDisk:cacheOnDisk];
                        }
 
                        dispatch_main_sync_safe(^{
                            if (!weakOperation.isCancelled) {
                                completedBlock(downloadedImage, nil, SDImageCacheTypeNone, finished, url);
                            }
                        });
                    }
                }
 
                if (finished) {
                    @synchronized (self.runningOperations) {
                        [self.runningOperations removeObject:operation];
                    }
                }
            }];
            operation.cancelBlock = ^{
                [subOperation cancel];
 
                @synchronized (self.runningOperations) {
                    [self.runningOperations removeObject:weakOperation];
                }
            };
        }
        else if (image) {
            dispatch_main_sync_safe(^{
                if (!weakOperation.isCancelled) {
                    completedBlock(image, nil, cacheType, YES, url);
                }
            });
            @synchronized (self.runningOperations) {
                [self.runningOperations removeObject:operation];
            }
        }
        else {
            // Image not in cache and download disallowed by delegate
            dispatch_main_sync_safe(^{
                if (!weakOperation.isCancelled) {
                    completedBlock(nil, nil, SDImageCacheTypeNone, YES, url);
                }
            });
            @synchronized (self.runningOperations) {
                [self.runningOperations removeObject:operation];
            }
        }
    }];
 
    return operation;
}

获取key对应的图片文件名

- (NSString *)cachedFileNameForKey:(NSString *)key {
    const char *str = [key UTF8String];
    if (str == NULL) {
        str = "";
    }
    unsigned char r[CC_MD5_DIGEST_LENGTH];
    CC_MD5(str, (CC_LONG)strlen(str), r);
    NSString *filename = [NSString stringWithFormat:@"%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%@",
                          r[0], r[1], r[2], r[3], r[4], r[5], r[6], r[7], r[8], r[9], r[10],
                          r[11], r[12], r[13], r[14], r[15], [[key pathExtension] isEqualToString:@""] ? @"" : [NSString stringWithFormat:@".%@", [key pathExtension]]];

    return filename;
}

判断一个图片的类型，是png还是jpng

- (void)storeImage:(UIImage *)image recalculateFromImage:(BOOL)recalculate imageData:(NSData *)imageData forKey:(NSString *)key toDisk:(BOOL)toDisk {
    if (!image || !key) {
        return;
    }
    // if memory cache is enabled
    if (self.shouldCacheImagesInMemory) {
        NSUInteger cost = SDCacheCostForImage(image);
        [self.memCache setObject:image forKey:key cost:cost];
    }

    if (toDisk) {
        dispatch_async(self.ioQueue, ^{
            NSData *data = imageData;

            if (image && (recalculate || !data)) {
#if TARGET_OS_IPHONE
                // We need to determine if the image is a PNG or a JPEG
                // PNGs are easier to detect because they have a unique signature (http://www.w3.org/TR/PNG-Structure.html)
                // The first eight bytes of a PNG file always contain the following (decimal) values:
                // 137 80 78 71 13 10 26 10

                // If the imageData is nil (i.e. if trying to save a UIImage directly or the image was transformed on download)
                // and the image has an alpha channel, we will consider it PNG to avoid losing the transparency
                int alphaInfo = CGImageGetAlphaInfo(image.CGImage);
                BOOL hasAlpha = !(alphaInfo == kCGImageAlphaNone ||
                                  alphaInfo == kCGImageAlphaNoneSkipFirst ||
                                  alphaInfo == kCGImageAlphaNoneSkipLast);
                BOOL imageIsPng = hasAlpha;

                // But if we have an image data, we will look at the preffix
                if ([imageData length] >= [kPNGSignatureData length]) {
                    imageIsPng = ImageDataHasPNGPreffix(imageData);
                }

                if (imageIsPng) {
                    data = UIImagePNGRepresentation(image);
                }
                else {
                    data = UIImageJPEGRepresentation(image, (CGFloat)1.0);
                }
#else
                data = [NSBitmapImageRep representationOfImageRepsInArray:image.representations usingType: NSJPEGFileType properties:nil];
#endif
            }

            [self storeImageDataToDisk:data forKey:key];
        });
    }
}

最后编辑于：2017.12.03 07:42:56

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