SDWebImage 簡介
1.提供了一個(gè)UIImageView的category用來加載網(wǎng)絡(luò)圖片并且對網(wǎng)絡(luò)圖片的緩存進(jìn)行管理
2.采用異步方式來下載網(wǎng)絡(luò)圖片
3.采用異步方式，使用memory＋disk來緩存網(wǎng)絡(luò)圖片挪蹭，自動(dòng)管理緩存
4.支持GIF動(dòng)畫
5.支持WebP格式
6.同一個(gè)URL的網(wǎng)絡(luò)圖片不會被重復(fù)下載
7.失效的URL不會被無限重試
8.耗時(shí)操作都在子線程雪隧，確保不會阻塞主線程
9.使用GCD和ARC
10.支持Arm64
SDWebImage 使用
1.使用IImageView+WebCache category來加載一張遠(yuǎn)程圖片
let url = URL(string: "http://f.hiphotos.baidu.com/image/h%3D200/sign=1e6c01ac9b13b07ea2bd57083cd69113/5fdf8db1cb134954ecbd6ee95e4e9258d0094a98.jpg")
imageV.sd_setImage(with: url)
2.加載一張遠(yuǎn)程圖片,在未完成加載時(shí)預(yù)留一張圖片
let placeholderImage = UIImage(named: "placeholderImage.png")
imageV.sd_setImage(with: url, placeholderImage: placeholderImage)
3.加載一張遠(yuǎn)程圖片,加載完成是執(zhí)行某些操作
imageV.sd_setImage(with: url) { (image, error, SDImageCacheTypeNone, url) in
print("OK")
}
SDWebImage 流程
下載選項(xiàng)
typedef NS_OPTIONS(NSUInteger, SDWebImageDownloaderOptions) {
SDWebImageDownloaderLowPriority = 1 << 0,
SDWebImageDownloaderProgressiveDownload = 1 << 1,
/**
* By default, request prevent the use of NSURLCache. With this flag, NSURLCache
* is used with default policies.
*/
SDWebImageDownloaderUseNSURLCache = 1 << 2,
/**
* Call completion block with nil image/imageData if the image was read from NSURLCache
* (to be combined with `SDWebImageDownloaderUseNSURLCache`).
*/
SDWebImageDownloaderIgnoreCachedResponse = 1 << 3,
/**
* In iOS 4+, continue the download of the image if the app goes to background. This is achieved by asking the system for
* extra time in background to let the request finish. If the background task expires the operation will be cancelled.
*/
SDWebImageDownloaderContinueInBackground = 1 << 4,
/**
* Handles cookies stored in NSHTTPCookieStore by setting
* NSMutableURLRequest.HTTPShouldHandleCookies = YES;
*/
SDWebImageDownloaderHandleCookies = 1 << 5,
/**
* Enable to allow untrusted SSL certificates.
* Useful for testing purposes. Use with caution in production.
*/
SDWebImageDownloaderAllowInvalidSSLCertificates = 1 << 6,
/**
* Put the image in the high priority queue.
*/
SDWebImageDownloaderHighPriority = 1 << 7,
};
可以看出，這些選項(xiàng)主要涉及到下載的優(yōu)先級复亏、緩存叽奥、后臺任務(wù)執(zhí)行鉴裹、cookie處理以認(rèn)證幾個(gè)方面。
緩存
為了減少網(wǎng)絡(luò)流量的消耗廷没，我們都希望下載下來的圖片緩存到本地糊饱，下次再去獲取同一張圖片時(shí)，可以直接從本地獲取颠黎，而不再從遠(yuǎn)程服務(wù)器獲取另锋。這樣做的另一個(gè)好處是提升了用戶體驗(yàn)滞项，用戶第二次查看同一幅圖片時(shí)，能快速從本地獲取圖片直接呈現(xiàn)給用戶夭坪。
SDWebImage提供了對圖片緩存的支持文判，而該功能是由SDImageCache類來完成的。該類負(fù)責(zé)處理內(nèi)存緩存及一個(gè)可選的磁盤緩存室梅。其中磁盤緩存的寫操作是異步的戏仓，這樣就不會對UI操作造成影響。
查詢圖片
- (UIImage *)imageFromMemoryCacheForKey:(NSString *)key;
- (UIImage *)imageFromDiskCacheForKey:(NSString *)key;
移除圖片
- (void)removeImageForKey:(NSString *)key;
- (void)removeImageForKey:(NSString *)key withCompletion:(SDWebImageNoParamsBlock)completion;
- (void)removeImageForKey:(NSString *)key fromDisk:(BOOL)fromDisk;
- (void)removeImageForKey:(NSString *)key fromDisk:(BOOL)fromDisk withCompletion:(SDWebImageNoParamsBlock)completion;
清空緩存圖片
- (void)clearMemory;
清空磁盤
- (void)clearDisk;
- (void)clearDiskOnCompletion:(SDWebImageNoParamsBlock)completion;
清理磁盤
刪除無效過期的圖片
- (void)cleanDisk;
- (void)cleanDiskWithCompletionBlock:(SDWebImageNoParamsBlock)completionBlock;
