iOS开发·由SDWebImage引发的知识点聚合与思考（最新呕心沥血之作）

self.imageView performSelector:@selector(setImage:) withObject:downloadedImage afterDelay:0 inModes:@[NSDefaultRunLoopMode]];

[self performSelectorOnMainThread:@selector(setImage:)
                       withObject:downloadedImage
                    waitUntilDone:YES
                            modes:@[NSDefaultRunLoopMode]];

- (void)cancelByProducingResumeData:(void (^)(NSData *resumeData))completionHandler;。

- (NSURLSessionDownloadTask *)downloadTaskWithResumeData:(NSData *)resumeData;，

self.downloadTask = [self.session downloadTaskWithResumeData:self.resumeData];​

// 创建下载路径
NSURL *url = [NSURL URLWithString:@"http://bmob-cdn-8782.b0.upaiyun.com/2017/01/17/c6b6bb1640e9ae9e80b221c454c4e90d.jpg"];
// 创建NSURLRequest请求
NSURLRequest *request = [NSURLRequest requestWithURL:url];
// 创建NSURLSession对象
NSURLSession *session = [NSURLSession sharedSession];
// 创建下载任务,其中location为下载的临时文件路径
NSURLSessionDownloadTask *downloadTask = [session downloadTaskWithURL:url completionHandler:^(NSURL *location, NSURLResponse *response, NSError *error) {
    // 文件将要移动到的指定目录
    NSString *documentsPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) firstObject];
    // 新文件路径
    NSString *newFilePath = [documentsPath stringByAppendingPathComponent:response.suggestedFilename]; 
    // 移动文件到新路径
    [[NSFileManager defaultManager] moveItemAtPath:location.path toPath:newFilePath error:nil];
}];
// 开始下载任务
[downloadTask resume];

// 创建下载路径
NSURL *url = [NSURL URLWithString:@"http://dldir1.qq.com/qqfile/QQforMac/QQ_V5.4.0.dmg"];
// 创建NSURLSession对象，并设计代理方法。其中NSURLSessionConfiguration为默认配置
NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration] delegate:self delegateQueue:[NSOperationQueue mainQueue]];   
// 创建任务
NSURLSessionDownloadTask *downloadTask = [session downloadTaskWithURL:url];
// 开始任务
[downloadTask resume];

#pragma mark <NSURLSessionDownloadDelegate> 实现方法
/**
 *  文件下载完毕时调用
 */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
didFinishDownloadingToURL:(NSURL *)location
{
    // 文件将要移动到的指定目录
    NSString *documentsPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) firstObject];
    // 新文件路径
    NSString *newFilePath = [documentsPath stringByAppendingPathComponent:@"QQ_V5.4.0.dmg"];
    
    NSLog(@"File downloaded to: %@",newFilePath);
    // 移动文件到新路径
    [[NSFileManager defaultManager] moveItemAtPath:location.path toPath:newFilePath error:nil];
}
/**
 *  每次写入数据到临时文件时，就会调用一次这个方法。可在这里获得下载进度
 *
 *  @param bytesWritten              这次写入的文件大小
 *  @param totalBytesWritten         已经写入沙盒的文件大小
 *  @param totalBytesExpectedToWrite 文件总大小
 */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
      didWriteData:(int64_t)bytesWritten
 totalBytesWritten:(int64_t)totalBytesWritten
totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
{
    
    // 下载进度
    self.progressView.progress = 1.0 * totalBytesWritten / totalBytesExpectedToWrite;
    self.progressLabel.text = [NSString stringWithFormat:@"当前下载进度:%.2f%%",100.0 * totalBytesWritten / totalBytesExpectedToWrite];
}

/**
 *  恢复下载后调用
 */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
 didResumeAtOffset:(int64_t)fileOffset
expectedTotalBytes:(int64_t)expectedTotalBytes1
{
    
}

[[NSFileManager defaultManager] copyItemAtPath:location.path toPath:path error:NULL];

// 移动文件到新路径
[[NSFileManager defaultManager] moveItemAtPath:location.path toPath:newFilePath error:nil];

//全局会话 创建 downLoadTask任务;
//参数location: 下载完成后文件路径 (需要我们重新指定)
[[[NSURLSession sharedSession] downloadTaskWithURL:url completionHandler:^(NSURL *location, NSURLResponse *response, NSError *error) {
    //重新指定路径
    NSString *path = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
    path = [path stringByAppendingPathComponent: fileName];
    //复制文件过去
    [[NSFileManager defaultManager] copyItemAtPath:location.path toPath:path error:NULL];
}] resume]; //启动任务

- (void)sd_setImageWithURL:(NSURL *)url{

- (void)sd_setImageWithURL:(NSURL *)url placeholderImage:(UIImage *)placeholder options:(SDWebImageOptions)options progress:(SDWebImageDownloaderProgressBlock)progressBlock completed:(SDWebImageCompletionBlock)completedBlock{

// balabala
id <SDWebImageOperation> operation = [SDWebImageManager.sharedManager downloadImageWithURL:url options:options progress:progressBlock completed:
// balabala

[self sd_setImageLoadOperation:operation forKey:@"UIImageViewImageLoad"];

- (id <SDWebImageOperation>)downloadImageWithURL:(NSURL *)url
                                         options:(SDWebImageOptions)options
                                        progress:(SDWebImageDownloaderProgressBlock)progressBlock
                                       completed:(SDWebImageCompletionWithFinishedBlock)completedBlock {

id <SDWebImageOperation> subOperation = [self.imageDownloader downloadImageWithURL:url options:downloaderOptions progress:progressBlock completed:^(UIImage *downloadedImage, NSData *data, NSError *error, BOOL finished) {

operation = [[wself.operationClass alloc] initWithRequest:request
                                                          options:options
                                                         progress:^(NSInteger receivedSize, NSInteger expectedSize) {

- (id)initWithRequest:(NSURLRequest *)request
              options:(SDWebImageDownloaderOptions)options
             progress:(SDWebImageDownloaderProgressBlock)progressBlock
            completed:(SDWebImageDownloaderCompletedBlock)completedBlock
            cancelled:(SDWebImageNoParamsBlock)cancelBlock {
    if ((self = [super init])) {
        _request = request;
        _shouldDecompressImages = YES;
        _shouldUseCredentialStorage = YES;
        _options = options;
        _progressBlock = [progressBlock copy];
        _completedBlock = [completedBlock copy];
        _cancelBlock = [cancelBlock copy];
        _executing = NO;
        _finished = NO;
        _expectedSize = 0;
        responseFromCached = YES; // Initially wrong until `connection:willCacheResponse:` is called or not called
    }
    return self;
}