从网页缓存中获取图片,将图片存放当本地文件夹中

- (void)webViewDidFinishLoad:(UIWebView *)webView{
    NSArray *a=[self getImgs];
    for (NSString *str in a) {
        NSURLCache *sharedCache = (NSURLCache *)[NSURLCache sharedURLCache];
        NSURLSession *session = [NSURLSession sharedSession];
        NSURLSessionDataTask *task = [session dataTaskWithURL:[NSURL URLWithString:str]];
        __block NSString *wstr = str;
        [sharedCache getCachedResponseForDataTask:task completionHandler:^(NSCachedURLResponse * _Nullable cachedResponse) {
            NSString *path = [NSString stringWithFormat:@"/Users/whde/Desktop/t/%@", [wstr lastPathComponent]];
            [cachedResponse.data writeToFile:path options:NSDataWritingAtomic error:nil];
             
        }];
    }
}
///  获取所有图片链接
- (NSArray *)getImgs
{
    NSMutableArray *arrImgURL = [[NSMutableArray alloc] init];
    for (int i = 0; i < [self nodeCountOfTag:@"img"]; i++) {
        NSString *jsString = [NSString stringWithFormat:@"document.getElementsByTagName('img')[%d].src", i];
        [arrImgURL addObject:[webView stringByEvaluatingJavaScriptFromString:jsString]];
    }
    return arrImgURL;
}
///  获取某个标签的结点个数
- (int)nodeCountOfTag:(NSString *)tag
{
    NSString *jsString = [NSString stringWithFormat:@"document.getElementsByTagName('%@').length", tag];
    int len = [[webView stringByEvaluatingJavaScriptFromString:jsString] intValue];
    return len;
}