ios -- cell的图片下载

1.面试题

1> 如何防止一个url对应的图片重复下载

* “cell下载图片思路 – 有沙盒缓存”

2> SDWebImage的默认缓存时长是多少？

* 1个星期

3> SDWebImage底层是怎么实现的？

* 上课PPT的“cell下载图片思路 – 有沙盒缓存”

2.SDWebImage

1> 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;

2> 内存处理：当app接收到内存警告时

/**

*  当app接收到内存警告

*/

- (void)applicationDidReceiveMemoryWarning:(UIApplication *)application

{

SDWebImageManager *mgr = [SDWebImageManager sharedManager];

// 1.取消正在下载的操作

[mgr cancelAll];

// 2.清除内存缓存

[mgr.imageCache clearMemory];

}

3> SDWebImageOptions

* 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