iOS开发——SDWebImage框架使用详解

迷南。 2022-07-24 05:30 331阅读 0赞

This library provides a category for UIImageView with support for remote images coming from the web.  
（这个类库提供一个UIImageView类别以支持加载来自网络的远程图片）

使用方法（已下代码是框架类README的实例代码）

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
    {
        static NSString *MyIdentifier = @"MyIdentifier";
    
        UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:MyIdentifier];
    
        if (cell == nil)
        {
            cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault
                                           reuseIdentifier:MyIdentifier] autorelease];
        }
    
        // 使用了框架里的setImageWithURL方法下载图片
        [cell.imageView setImageWithURL:[NSURL URLWithString:@"http://www.domain.com/path/to/image.jpg"]
                       placeholderImage:[UIImage imageNamed:@"placeholder.png"]];
    
        cell.textLabel.text = @"My Text";
        return cell;
    }

SDWebImage中的一些常用方法：

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

常用的SDWebImageOptions选项：  
SDWebImageRetryFailed : 下载失败后，会自动重新下载  
SDWebImageLowPriority : 当正在进行UI交互时，自动暂停内部的一些下载操作  
SDWebImageRetryFailed | SDWebImageLowPriority : 拥有上面2个功能

下面是详解所有SDWebImageOptions的所有选项：

typedef NS_OPTIONS(NSUInteger, SDWebImageOptions) {
        /**
         * By default, when a URL fail to be downloaded, the URL is blacklisted so the library won't keep trying.
         * 默认情况下，当一个 URL 下载失败，会将该 URL 放在黑名单中，不再尝试下载
         *
         * This flag disable this blacklisting.
         * 此标记取消黑名单
         */
        SDWebImageRetryFailed = 1 << 0,
    
        /**
         * By default, image downloads are started during UI interactions, this flags disable this feature,
         * 默认情况下，在 UI 交互时也会启动图像下载，此标记取消这一特性
         *
         * leading to delayed download on UIScrollView deceleration for instance.
         * 会推迟到滚动视图停止滚动之后再继续下载(这个注释是假的！)
         */
        SDWebImageLowPriority = 1 << 1,
    
        /**
         * This flag disables on-disk caching
         * 此标记取消磁盘缓存，只有内存缓存
         */
        SDWebImageCacheMemoryOnly = 1 << 2,
    
        /**
         * This flag enables progressive download, the image is displayed progressively during download as a browser would do.
         * 此标记允许渐进式下载，就像浏览器中那样，下载过程中，图像会逐步显示出来
         *
         * By default, the image is only displayed once completely downloaded.
         * 默认情况下，图像会在下载完成后一次性显示
         */
        SDWebImageProgressiveDownload = 1 << 3,
    
        /**
         * Even if the image is cached, respect the HTTP response cache control, and refresh the image from remote location if needed.
         * 即使图像被缓存，遵守 HTPP 响应的缓存控制，如果需要，从远程刷新图像
         *
         * The disk caching will be handled by NSURLCache instead of SDWebImage leading to slight performance degradation.
         * 磁盘缓存将由 NSURLCache 处理，而不是 SDWebImage，这会对性能有轻微的影响
         *
         * This option helps deal with images changing behind the same request URL, e.g. Facebook graph api profile pics.
         * 此选项有助于处理同一个请求 URL 的图像发生变化
         *
         * If a cached image is refreshed, the completion block is called once with the cached image and again with the final image.
         * 如果缓存的图像被刷新，会调用一次 completion block，并传递最终的图像
         *
         * Use this flag only if you can't make your URLs static with embeded cache busting parameter.
         * 仅在无法使用嵌入式缓存清理参数确定图像 URL 时，使用此标记
         */
        SDWebImageRefreshCached = 1 << 4,
    
        /**
         * In iOS 4+, continue the download of the image if the app goes to background. This is achieved by asking the system for
         * 在 iOS 4+，当 App 进入后台后仍然会继续下载图像。这是向系统请求额外的后台时间以保证下载请求完成的
         *
         * extra time in background to let the request finish. If the background task expires the operation will be cancelled.
         * 如果后台任务过期，请求将会被取消
         */
        SDWebImageContinueInBackground = 1 << 5,
    
        /**
         * Handles cookies stored in NSHTTPCookieStore by setting
         * 通过设置
         * NSMutableURLRequest.HTTPShouldHandleCookies = YES;
         * 处理保存在 NSHTTPCookieStore 中的 cookies
         */
        SDWebImageHandleCookies = 1 << 6,
    
        /**
         * Enable to allow untrusted SSL ceriticates.
         * 允许不信任的 SSL 证书
         *
         * Useful for testing purposes. Use with caution in production.
         * 可以出于测试目的使用，在正式产品中慎用
         */
        SDWebImageAllowInvalidSSLCertificates = 1 << 7,
    
        /**
         * By default, image are loaded in the order they were queued. This flag move them to
         * 默认情况下，图像会按照在队列中的顺序被加载，此标记会将它们移动到队列前部立即被加载
         *
         * the front of the queue and is loaded immediately instead of waiting for the current queue to be loaded (which
         * 而不是等待当前队列被加载，等待队列加载会需要一段时间
         * could take a while).
         */
        SDWebImageHighPriority = 1 << 8,
    
        /**
         * By default, placeholder images are loaded while the image is loading. This flag will delay the loading
         * 默认情况下，在加载图像时，占位图像已经会被加载。而此标记会延迟加载占位图像，直到图像已经完成加载
         *
         * of the placeholder image until after the image has finished loading.
         */
        SDWebImageDelayPlaceholder = 1 << 9,
    
        /**
         * We usually don't call transformDownloadedImage delegate method on animated images,
         * 通常不会在可动画的图像上调用 transformDownloadedImage 代理方法，因为大多数转换代码会破坏动画文件
         *
         * as most transformation code would mangle it.
         * Use this flag to transform them anyway.
         * 使用此标记尝试转换
         */
        SDWebImageTransformAnimatedImage = 1 << 10,
    };

看到这，你已经可以用SDWebimage进行图片缓存了。