源码解析ios开发SDWebImage方法
<div id="navCategory"><h5 class="catalogue">目录</h5><ul class="first_class_ul"><li>引言</li><li>源码解析</li><ul class="second_class_ul"><li>字典操作</li><li>看一下调用下载函数前的实例化过程</li><ul class="third_class_ul"><li>快速查找缓存的方法回调</li></ul></ul><li>开始进入查找函数</li><ul class="second_class_ul"></ul><li>总结一下函数调用</li><ul class="second_class_ul"><li>1.先调用</li><ul class="third_class_ul"></ul><li>2.设置图片</li><ul class="third_class_ul"></ul></ul></ul></div><p class="maodian"></p><h2>引言</h2><p>在着手写第二篇的时候，发现这个SDWebimage确实吧NSOperation用的太美了。确实可能帮你理解<code>NSOperation</code>和<code>NSOperationQueue</code>,当然还有Block的队列。还有一个<code>GCD</code>。</p>
<p>各位看官在看的时候可以着重的看看他的<code>operatinQueue</code>的队列。看看是怎么添加到队列的以及是怎么移除队列。在后面的文章就会提到他是怎么执行的。 还要注重看的就是以前用的<code>NSURLConnection</code>而现在用的<code>NSURLSession</code>下来了</p>
<p>最近在面试，发现有人问这个组件，所有读一读，应付一下面试吧！！</p>
<p class="maodian"></p><h2>源码解析</h2>
<p>废话不多说看源码。</p>
<ul><li>1:在组件中提供了很多类似这样的方法</li></ul>
<div class="jb51code"><pre class="brush:cpp;">- (void)sd_setImageWithURL:(nullable NSURL *)url;
- (void)sd_setImageWithURL:(nullable NSURL *)url
placeholderImage:(nullable UIImage *)placeholder;
</pre></div>
<ul><li>2:于是乎所有的方法都会调用下面的这个方法</li></ul>
<div class="jb51code"><pre class="brush:cpp;">- (void)sd_internalSetImageWithURL:(nullable NSURL *)url
placeholderImage:(nullable UIImage *)placeholder
options:(SDWebImageOptions)options
operationKey:(nullable NSString *)operationKey
setImageBlock:(nullable SDSetImageBlock)setImageBlock
progress:(nullable SDWebImageDownloaderProgressBlock)progressBlock
completed:(nullable SDExternalCompletionBlock)completedBlock
</pre></div>
<ul><li>3：下面具体阅读代码 第一行执行的代码</li></ul>
<div class="jb51code"><pre class="brush:cpp;">//********1: 所有的设置控件图片都是经过该方法*******
NSString *validOperationKey = operationKey ?: NSStringFromClass();
//********2: 取消当前控件正在operations的队列*******
;
</pre></div>
<p>解析：</p>
<p>1.在第一行创建了<code>validOperationKey</code>的operationKey，是以当前扩展的类名命名。</p>
<p>2.执行<code>sd_cancelImageLoadOperationWithKey</code>方法</p>
<div class="jb51code"><pre class="brush:cpp;">- (void)sd_cancelImageLoadOperationWithKey:(nullable NSString *)key {
// Cancel in progress downloader from queue
/**
* 在该对象中，用runtime手动的添加一个字典属性。
### 说一下这里的operationDictionary
### 该字典的value是下载的操作，然而key是对视图和操作来做的标识字符串
*/
SDOperationsDictionary *operationDictionary = ;
/*
* 在生成字典中的都是新的，所有都没有数据
*/
id operations = operationDictionary;
if (operations) {
if (]) {
for (id &lt;SDWebImageOperation&gt; operation in operations) {
if (operation) {
;
}
}
} else if (){
[(id&lt;SDWebImageOperation&gt;) operations cancel];
}
;
}
}
</pre></div>
<p class="maodian"></p><h3>字典操作</h3>
<p>在看一下去字典操作<code></code></p>
<div class="jb51code"><pre class="brush:cpp;">- (SDOperationsDictionary *)operationDictionary {
/**
### 这里有一个疑问？
这样创建出来的字典每一次都是新的
虽然用了 static char loadOperationKey，但是没一次创建的地址都是新的，并且该字典还是空的。
创建完成之后都直接返回了。不知道每次创建的都是新的并且还是空的字典，这样的开销会很大的？？！！！，也希望各位看官给予解答啊？？？
*/
SDOperationsDictionary *operations = objc_getAssociatedObject(self, &amp;loadOperationKey);
// 创建成功返回该字典，直接把该字典当做属性返回
if (operations) {
return operations;
}
operations = ;
objc_setAssociatedObject(self, &amp;loadOperationKey, operations, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
return operations;
}
</pre></div>
<p>看到这里我们在返回继续看 这个函数的代码有点长，耐心看完啊。。。</p>
<div class="jb51code"><pre class="brush:cpp;">- (void)sd_internalSetImageWithURL:(nullable NSURL *)url
placeholderImage:(nullable UIImage *)placeholder
options:(SDWebImageOptions)options
operationKey:(nullable NSString *)operationKey
setImageBlock:(nullable SDSetImageBlock)setImageBlock
progress:(nullable SDWebImageDownloaderProgressBlock)progressBlock
completed:(nullable SDExternalCompletionBlock)completedBlock {
//********1: 所有的设置控件图片都是经过该方法*******
NSString *validOperationKey = operationKey ?: NSStringFromClass();
/**2: 取消当前控件正在operations的队列
* 至于为什么在该控件下载前都要清空该控件对应的所有的下载队列？
* 可能是，如果要给控件赋值新的图片的话，之前所有的操作都和当前的操作无关，所有就取消吧
*******/
;
objc_setAssociatedObject(self, &amp;imageURLKey, url, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
/**3：设置占位图片*/
/**这里的意思就是options参数不是SDWebImageDelayPlaceholder,就执行以下操作 */
if (!(options &amp; SDWebImageDelayPlaceholder)) {
/**
* 注意这的里宏定义
* #ifndef dispatch_main_async_safe
* #define dispatch_main_async_safe(block)\
* if (strcmp(dispatch_queue_get_label(DISPATCH_CURRENT_QUEUE_LABEL), dispatch_queue_get_label(dispatch_get_main_queue())) == 0) {\
* block();\
* } else {\
* dispatch_async(dispatch_get_main_queue(), block);\
* }
* #endif
可以看出都把block方法主线程中去执行。
应为在系统里，只能有一个线程去执行UI的更新，那就是主线程。
如果能在其他线程更新，那这世界就乱了，像了解
更仔细的问题可以关注www.osjoin.com查看是为什么！
*/
dispatch_main_async_safe(^{
/**设置占位图placeholder*/
;
});
}
/**4：菊花提示*/
if (url) {
// check if activityView is enabled or not
if () {
;
}
__weak __typeof(self)wself = self;
/**5:下载图片
* 进入下载图片最重要的函数也是核心的函数了
这个函数关联的函数较多，先简单过一下。
*/
id &lt;SDWebImageOperation&gt; operation = [SDWebImageManager.sharedManager loadImageWithURL:url options:options progress:progressBlock completed:^(UIImage *image, NSData *data, NSError *error, SDImageCacheType cacheType, BOOL finished, NSURL *imageURL) {
__strong __typeof (wself) sself = wself;
;
if (!sself) {
return;
}
dispatch_main_async_safe(^{
if (!sself) {
return;
}
if (image &amp;&amp; (options &amp; SDWebImageAvoidAutoSetImage) &amp;&amp; completedBlock) {
completedBlock(image, error, cacheType, url);
return;
} else if (image) {
;
;
} else {
if ((options &amp; SDWebImageDelayPlaceholder)) {
;
;
}
}
if (completedBlock &amp;&amp; finished) {
completedBlock(image, error, cacheType, url);
}
});
}];
/**将行的下操作放到uiview的下载队列中的自定义的字典中去*/
;
} else {
dispatch_main_async_safe(^{
;
if (completedBlock) {
NSError *error = ;
completedBlock(nil, error, SDImageCacheTypeNone, url);
}
});
}
}
</pre></div>
<p class="maodian"></p><h3>看一下调用下载函数前的实例化过程</h3>
<p>这个loadImageWithURL函数在SDWebImageManager，并且是用单列调用,</p>
<div class="jb51code"><pre class="brush:cpp;">+ (nonnull instancetype)sharedManager {
static dispatch_once_t once;
static id instance;
dispatch_once(&amp;once, ^{
instance = ;
});
return instance;
}
- (nonnull instancetype)init {
/**
###此处有其他重要配置，下一篇文章解读
###此处有其他重要配置，下一篇文章解读
###此处有其他重要配置，下一篇文章解读
*/
SDImageCache *cache = ;
SDWebImageDownloader *downloader = ;
return ;
}
- (nonnull instancetype)initWithCache:(nonnull SDImageCache *)cache downloader:(nonnull SDWebImageDownloader *)downloader {
if ((self = )) {
_imageCache = cache;
_imageDownloader = downloader;
/**这里的failedURLS是NSSet也就没重复的属性*/
_failedURLs = ;
_runningOperations = ;
}
return self;
}
</pre></div>
<p>上面都是初始化的操作，然后看下面的函数</p>
<div class="jb51code"><pre class="brush:cpp;">- (id <SDWebImageOperation>)loadImageWithURL:(nullable NSURL *)url
options:(SDWebImageOptions)options
progress:(nullable SDWebImageDownloaderProgressBlock)progressBlock
completed:(nullable SDInternalCompletionBlock)completedBlock {
// Invoking this method without a completedBlock is pointless
NSAssert(completedBlock != nil, @"If you mean to prefetch the image, use - 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.
/**
这里防止用户输入的类型错误，转换一下
*/
if () {
url = ;
}
// Prevents app crashing on argument type error like sending NSNull instead of NSURL
/*! 如果转换失败，url为nil 返回 */
if (!) {
url = nil;
}
/**5.1:搞一个新的下载队列*/
/*! 这里就又__block和__weak的用法区别
这里简单说说一下
1:__block,在block函数里可以修改和阅读
2:__weak可以避免循环引用，在给他设置新数据的时候，设置方法既不保留新值，也不释放旧值
*/
/*! 说一下SDWebImageCombinedOperation
他拥有了一个缓存队列和一个能取消执行的block，并且还遵守了SDWebImageOperation一个协议
*/
__block SDWebImageCombinedOperation *operation = ;
__weak SDWebImageCombinedOperation *weakOperation = operation;
/**5.2判断URL是否是下载失败的url*/
BOOL isFailedUrl = NO;
if (url) {
/*! 创建一个互斥锁防止有其他线程同时修改该对象 */
@synchronized (self.failedURLs) {
isFailedUrl = ;
}
}
/**
* 5.3url不存在或者下载失败的url 则不在继续下载队列
* 返回一个completedBlock
*/
if (url.absoluteString.length == 0 || (!(options & SDWebImageRetryFailed) && isFailedUrl)) {
url:url];
return operation;
}
/**5.4把url添加在下载队列
把operation加入到self.runningOperations的数组里面,
并创建一个互斥线程锁来保护这个操作
*/
@synchronized (self.runningOperations) {
;
}
/*! 获取image的url对应的key */
NSString *key = ;
/**5.5快速查找***缓存*****/
operation.cacheOperation = [self.imageCache queryCacheOperationForKey:key done:^(UIImage *cachedImage, NSData *cachedData, SDImageCacheType cacheType) {
/**
* 这里的状态改变，在sd_cancelImageLoadOperationWithKey方法中调用代理函数时会改变该状态cancel
* 如果该队列是取消状态，直接从下载队列中移除，此处有一个安全锁
*/
if (operation.isCancelled) {
;
return;
}
/**下载完成之后执行图片转换处理和缓存操作**/
//条件1:在缓存中没有找到图片或者options选项里面包含了SDWebImageRefreshCached(这两项都需要进行请求网络图片的)
//条件2:代理允许下载,SDWebImageManagerDelegate的delegate不能响应imageManager:shouldDownloadImageForURL:方法或者能响应方法且方法返回值为YES.也就是没有实现这个方法就是允许的,如果实现了的话,返回YES才是允许
if ((!cachedImage || options & SDWebImageRefreshCached) &&
(! || )) {
//如果在缓存中找到了image且options选项包含SDWebImageRefreshCached,先在主线程完成一次回调,使用的是缓存中找的图片
if (cachedImage && options & SDWebImageRefreshCached) {
// If image was found in the cache but 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.
/** 如果在缓存中找到了image但是设置了SDWebImageRefreshCached选项，传递缓存的image，同时尝试重新下载它来让NSURLCache有机会接收服务器端的更新
dispatch_main_async_safe(^{
if (operation && !operation.isCancelled && completionBlock) {
completionBlock(image, data, error, cacheType, finished, url);
}
});
*/
;
}
// 如果没有在缓存中找到image 或者设置了需要请求服务器刷新的选项,则仍需要下载
// download if no image or requested to refresh anyway, and download allowed by delegate
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 (options & SDWebImageScaleDownLargeImages) downloaderOptions |= SDWebImageDownloaderScaleDownLargeImages;
if (cachedImage && options & SDWebImageRefreshCached) {
// force progressive off if image already cached but forced refreshing
// 如果image已经被缓存但是设置了需要请求服务器刷新的选项，强制关闭渐进式选项
downloaderOptions &= ~SDWebImageDownloaderProgressiveDownload;
// ignore image read from NSURLCache if image if cached but force refreshing
// 如果image已经被缓存但是设置了需要请求服务器刷新的选项，忽略从NSURLCache读取的image
downloaderOptions |= SDWebImageDownloaderIgnoreCachedResponse;
}
/**如果在缓存和硬盘上都没查到url对应的图片
***则进行图片下载
*/
/*! 进入下载操作就是2.2中的操作了*/
SDWebImageDownloadToken *subOperationToken = [self.imageDownloader downloadImageWithURL:url
options:downloaderOptions
progress:progressBlock
completed:^(UIImage *downloadedImage,
NSData *downloadedData,
NSError *error,
BOOL finished) {
__strong __typeof(weakOperation) strongOperation = weakOperation;
/*! 如果为取消状态，啥也不错，闲着 */
if (!strongOperation || strongOperation.isCancelled) {
// Do nothing if the operation was cancelled
// 不用做任何事情，如果是取消状态
// 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
//如果我们调用completedBlock,这个block会和另外一个completedBlock争夺一个对象,因此这个block被调用后会覆盖新的数据
} else if (error) {
//进行完成回调
;
if ( error.code != NSURLErrorNotConnectedToInternet
&& error.code != NSURLErrorCancelled
&& error.code != NSURLErrorTimedOut
&& error.code != NSURLErrorInternationalRoamingOff
&& error.code != NSURLErrorDataNotAllowed
&& error.code != NSURLErrorCannotFindHost
&& error.code != NSURLErrorCannotConnectToHost) {
//将失败的url添加到failedURLS的set中去
@synchronized (self.failedURLs) {
;
}
}
}
else {
//如果有重试状态,将url从失败列表中移除
if ((options & SDWebImageRetryFailed)) {
@synchronized (self.failedURLs) {
;
}
}
BOOL cacheOnDisk = !(options & SDWebImageCacheMemoryOnly);
//options包含了SDWebImageRefreshCached选项,且缓存中找到了image且没有下载成功
if (options & SDWebImageRefreshCached && cachedImage && !downloadedImage) {
// Image refresh hit the NSURLCache cache, do not call the completion block
} else if (
//图片下载成功并且 设置了需要变形Image的选项且变形的代理方法已经实现
downloadedImage &&
(!downloadedImage.images || (options & SDWebImageTransformAnimatedImage)) &&
) {
/**
* dispatch_get_global_queue创建的一个//全局队列异步队列执行
*/
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
//调用代理方法完成图片transform
UIImage *transformedImage = ;
if (transformedImage && finished) {
BOOL imageWasTransformed = !;
// pass nil if the image was transformed, so we can recalculate the data from the image
//对已经transform的图片进行缓存
;
}
/*! 回到主线的调度 */
;
});
} else {
//如果没有图片transform的需求并且图片下载完成且图片存在就直接缓存
if (downloadedImage && finished) {
;
}
/*! 回到主线的调度 */
;
}
}
/**
* 从正在进行的操作列表中移除这组合操作
* 此处有一个安全锁保证线程安全
*/
if (finished) {
;
}
}];
/**取消的回调*/
operation.cancelBlock = ^{
;
__strong __typeof(weakOperation) strongOperation = weakOperation;
;
};
//在缓存中找到图片(代理不允许下载 或者没有设置SDWebImageRefreshCached选项满足至少一项)
} else if (cachedImage) {
__strong __typeof(weakOperation) strongOperation = weakOperation;
;
;
} else {
//缓存中没有扎到图片且代理不允许下载
// Image not in cache and download disallowed by delegate
__strong __typeof(weakOperation) strongOperation = weakOperation;
;
;
}
}];
return operation;
}
</pre></div>
<p>这个函数就进入了SDWebimage缓存的策略了。</p>
<p>先说一下他的这一个策略缓存。</p>
<p>*1：大家都是SDWebiamge都是先从缓存上查找，如果有就直接显示</p>
<p>*2：如果不存在就在沙盒中查找 </p>
<ul><li>*2.1如果存在，则把沙盒中的图片添加到imageCache中，取出显示 </li><li>*2.2 如果不存在在显示占位图，根据URL在operationCache是否存在下载操作 </li></ul>
<p>*2.2.1 如果存在，说明该图片正在下载。</p>
<p>*2.2.2如果不存在，创建图片下载操作，放到operationCache中</p>
<ul><li>* 2.3 下载完成，将当前操作队列从operationCache中移除。并将下载的图片的添加在imageCache中。显示</li></ul>
<p>先慢慢体会一下。。。（停留30秒）</p>
<p class="maodian"></p><h2>开始进入查找函数</h2>
<div class="jb51code"><pre class="brush:cpp;">- (nullable NSOperation *)queryCacheOperationForKey:(nullable NSString *)key done:(nullable SDCacheQueryCompletedBlock)doneBlock {
/**从缓存中查找图片开始*/
/*! 检查key是否为空（URL） */
if (!key) {
if (doneBlock) {
doneBlock(nil, nil, SDImageCacheTypeNone);
}
return nil;
}
// 先检查缓存--内存上的数据
// First check the in-memory cache...
UIImage *image = ;
if (image) {
/**从内存在检查到有图片**/
NSData *diskData = nil;
if () {
diskData = ;
}
/**如果有直接返回在view上显示*/
if (doneBlock) {
doneBlock(image, diskData, SDImageCacheTypeMemory);
}
return nil;
}
/**如果内存上没有数据，则在硬盘上查找，如果找到了该图片，就放到缓存上用doneBlock完成回调**/
/*! 这一块创建了异步队列
这里的self.ioQueue是这样定义的
****@property (strong, nonatomic, nullable) dispatch_queue_t ioQueue;
****这里开始了串行的队列去处理硬盘上的缓存
*/
NSOperation *operation = ;
dispatch_async(self.ioQueue, ^{
/**如果是取消的 就直接返回*/
if (operation.isCancelled) {
// do not call the completion if cancelled
return;
}
/*! 开了手动释放池 */
@autoreleasepool {
/**从磁盘中读取图片*/
/*! 根据url去硬盘上查找数据 */
NSData *diskData = ;
UIImage *diskImage = ;
if (diskImage && self.config.shouldCacheImagesInMemory) {
NSUInteger cost = SDCacheCostForImage(diskImage);
/**如果在硬盘中读取到图片，则把沙盒中的图片放到Cache中*/
//self.memCache是NSCache创建的一个对象
;
}
if (doneBlock) {
/*! 在主线程放回数据 */
dispatch_async(dispatch_get_main_queue(), ^{
doneBlock(diskImage, diskData, SDImageCacheTypeDisk);
});
}
}
});
return operation;
}
</pre></div>
<p class="maodian"></p><h4>快速查找缓存的方法回调</h4>
<p>看完该函数以后在回到上面的看这个快速查找缓存的方法回调</p>
<div class="jb51code"><pre class="brush:cpp;">operation.cacheOperation = [self.imageCache queryDiskCacheForKey:key done:^(UIImage *image, SDImageCacheType cacheType) {
if (operation.isCancelled) {
@synchronized (self.runningOperations) {
;
}
return;
}
if ((!image || options & SDWebImageRefreshCached) && (! || )) {
//如果在缓存中找到了image且options选项包含SDWebImageRefreshCached,先在主线程完成一次回调,使用的是缓存中找的图片
if (image && options & SDWebImageRefreshCached) {
dispatch_main_sync_safe(^{
// 如果在缓存中找到了image但是设置了SDWebImageRefreshCached选项，传递缓存的image，同时尝试重新下载它来让NSURLCache有机会接收服务器端的更新
completedBlock(image, nil, cacheType, YES, url);
});
}
// 如果没有在缓存中找到image 或者设置了需要请求服务器刷新的选项,则仍需要下载
SDWebImageDownloaderOptions downloaderOptions = 0;
//开始各种options的判断
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) {
// 如果image已经被缓存但是设置了需要请求服务器刷新的选项，强制关闭渐进式选项
downloaderOptions &= ~SDWebImageDownloaderProgressiveDownload;
// 如果image已经被缓存但是设置了需要请求服务器刷新的选项，忽略从NSURLCache读取的image
downloaderOptions |= SDWebImageDownloaderIgnoreCachedResponse;
}
//创建下载操作,先使用self.imageDownloader下载
id <SDWebImageOperation> subOperation = [self.imageDownloader downloadImageWithURL:url options:downloaderOptions progress:progressBlock completed:^(UIImage *downloadedImage, NSData *data, NSError *error, BOOL finished) {
__strong __typeof(weakOperation) strongOperation = weakOperation;
if (!strongOperation || strongOperation.isCancelled) {
// Do nothing if the operation was cancelled
//如果操作取消了,不做任何事情
// 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
//如果我们调用completedBlock,这个block会和另外一个completedBlock争夺一个对象,因此这个block被调用后会覆盖新的数据
}
else if (error) {
//进行完成回调
dispatch_main_sync_safe(^{
if (strongOperation && !strongOperation.isCancelled) {
completedBlock(nil, error, SDImageCacheTypeNone, finished, url);
}
});
//将url添加到失败列表里面
if ( error.code != NSURLErrorNotConnectedToInternet
&& error.code != NSURLErrorCancelled
&& error.code != NSURLErrorTimedOut
&& error.code != NSURLErrorInternationalRoamingOff
&& error.code != NSURLErrorDataNotAllowed
&& error.code != NSURLErrorCannotFindHost
&& error.code != NSURLErrorCannotConnectToHost) {
@synchronized (self.failedURLs) {
;
}
}
}
else {
//如果设置了下载失败重试,将url从失败列表中去掉
if ((options & SDWebImageRetryFailed)) {
@synchronized (self.failedURLs) {
;
}
}
BOOL cacheOnDisk = !(options & SDWebImageCacheMemoryOnly);
//options包含了SDWebImageRefreshCached选项,且缓存中找到了image且没有下载成功
if (options & SDWebImageRefreshCached && image && !downloadedImage) {
// Image refresh hit the NSURLCache cache, do not call the completion block
// 图片刷新遇到了NSSURLCache中有缓存的状况，不调用完成回调。
}
//图片下载成功并且 设置了需要变形Image的选项且变形的代理方法已经实现
else if (downloadedImage && (!downloadedImage.images || (options & SDWebImageTransformAnimatedImage)) && ) {
//全局队列异步执行 dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
//调用代理方法完成图片transform
UIImage *transformedImage = ;
if (transformedImage && finished) {
BOOL imageWasTransformed = !;
//对已经transform的图片进行缓存
;
}
//主线程执行完成回调
dispatch_main_sync_safe(^{
if (strongOperation && !strongOperation.isCancelled) {
completedBlock(transformedImage, nil, SDImageCacheTypeNone, finished, url);
}
});
});
}
//如果没有图片transform的需求并且图片下载完成且图片存在就直接缓存
else {
if (downloadedImage && finished) {
;
}
//主线程完成回调
dispatch_main_sync_safe(^{
if (strongOperation && !strongOperation.isCancelled) {
completedBlock(downloadedImage, nil, SDImageCacheTypeNone, finished, url);
}
});
}
}
if (finished) {
// 从正在进行的操作列表中移除这组合操作
@synchronized (self.runningOperations) {
if (strongOperation) {
;
}
}
}
}];
//设置组合操作取消得得回调
operation.cancelBlock = ^{
;
@synchronized (self.runningOperations) {
__strong __typeof(weakOperation) strongOperation = weakOperation;
if (strongOperation) {
;
}
}
};
}
//处理其他情况
//case1.在缓存中找到图片(代理不允许下载 或者没有设置SDWebImageRefreshCached选项满足至少一项)
else if (image) {
//完成回调
dispatch_main_sync_safe(^{
__strong __typeof(weakOperation) strongOperation = weakOperation;
if (strongOperation && !strongOperation.isCancelled) {
completedBlock(image, nil, cacheType, YES, url);
}
});
//从正在进行的操作列表中移除组合操作
@synchronized (self.runningOperations) {
;
}
}
//case2:缓存中没有扎到图片且代理不允许下载
else {
//主线程执行完成回调
dispatch_main_sync_safe(^{
__strong __typeof(weakOperation) strongOperation = weakOperation;
if (strongOperation && !weakOperation.isCancelled) {
completedBlock(nil, nil, SDImageCacheTypeNone, YES, url);
}
});
//从正在执行的操作列表中移除组合操作
@synchronized (self.runningOperations) {
;
}
}
}];
</pre></div>
<p class="maodian"></p><h2>总结一下函数调用</h2>
<p class="maodian"></p><h3>1.先调用</h3>
<div class="jb51code"><pre class="brush:cpp;">- (void)sd_setImageWithURL:(nullable NSURL *)url
placeholderImage:(nullable UIImage *)placeholder;
</pre></div>
<p class="maodian"></p><h3>2.设置图片</h3>
<div class="jb51code"><pre class="brush:cpp;">- (void)sd_internalSetImageWithURL:(nullable NSURL *)url
placeholderImage:(nullable UIImage *)placeholder
options:(SDWebImageOptions)options
operationKey:(nullable NSString *)operationKey
setImageBlock:(nullable SDSetImageBlock)setImageBlock
progress:(nullable SDWebImageDownloaderProgressBlock)progressBlock
completed:(nullable SDExternalCompletionBlock)completedBlock
</pre></div>
<ul><li>2.1 取消该控件对应的之前的所有的下载操作</li></ul>
<div class="jb51code"><pre class="brush:cpp;">- (void)sd_cancelImageLoadOperationWithKey:(nullable NSString *)key;
</pre></div>
<ul><li>2.2 开始根据图片的url做为key去查找</li></ul>
<div class="jb51code"><pre class="brush:cpp;">- (id <SDWebImageOperation>)loadImageWithURL:(nullable NSURL *)url
options:(SDWebImageOptions)options
progress:(nullable SDWebImageDownloaderProgressBlock)progressBlock
completed:(nullable SDInternalCompletionBlock)completedBlock
</pre></div>
<p>2.2.1 查找内存和硬盘上的缓存</p>
<div class="jb51code"><pre class="brush:cpp;">- (nullable NSOperation *)queryCacheOperationForKey:(nullable NSString *)key done:(nullable SDCacheQueryCompletedBlock)doneBlock;
</pre></div>
<ul><li>2.3 创建下载队列下载图片</li></ul>
<div class="jb51code"><pre class="brush:cpp;">- (nullable SDWebImageDownloadToken *)downloadImageWithURL:(nullable NSURL *)url
options:(SDWebImageDownloaderOptions)options
progress:(nullable SDWebImageDownloaderProgressBlock)progressBlock
completed:(nullable SDWebImageDownloaderCompletedBlock)completedBlock;
</pre></div>
<ul><li>2.4 最后将进行的操作，放到view对应的opationsDicaionary的字典中。记录当前的操作队列</li></ul>
<div class="jb51code"><pre class="brush:cpp;">- (void)sd_setImageLoadOperation:(nullable id)operation forKey:(nullable NSString *)key</pre></div>
<p>以上就是源码解析ios开发SDWebImage方法的详细内容，更多关于ios SDWebImage方法的资料请关注琼殿技术社区其它相关文章！</p>
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