iOS图片加载（imageData）

Question

微信和微博分享的对于原生封装的加载图片的方法如下：

+ (NSData )loadImageDataWithImageUrl:(NSString )urlString {

NSURL *url = [NSURL URLWithString:urlString];
SDImageCache *imageCache = [SDImageCache sharedImageCache];
UIImage *image = nil;
NSData *imageData = nil;
//有缓存，从缓存中去图片

if ([imageCache imageFromMemoryCacheForKey:urlString]) {

image = [imageCache imageFromMemoryCacheForKey:urlString];

imageData = UIImageJPEGRepresentation(image, 1.0);

}else if ([imageCache imageFromDiskCacheForKey:urlString]) {

image = [imageCache imageFromDiskCacheForKey:urlString];

imageData = UIImageJPEGRepresentation(image, 1.0);

}else{

//缓存中没有图片去下载
imageData = [NSData dataWithContentsOfURL:url];
}
return imageData;
}

现在 ： imageData = [NSData dataWithContentsOfURL:url]; 这句代码的效率极低，导致分享会很慢，现在求优化方法，望各位大神指点！

Answer 1

Didn’t you write: There is no download in the cache... everything is downloaded. It must be very slow using this basic method.
I don’t quite understand, since SDWebImage is used, why do we need to write another method to loadImageData

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Supplement

Download the image UIImage and then convert it into data
Isn’t your cache the same thing as taking out the image and converting it into data?

Answer 2

@Curiousity If it is not in the cache, download it. Is there a better method than imageData = [NSData dataWithContentsOfURL:url]; ? I have looked at SDWebImage, but there is no way to download imageData directly!

Answer 3

Try this asynchronous
SDWebImageDownloader.h

- (id <SDWebImageOperation>)downloadImageWithURL:(NSURL *)url
                                         options:(SDWebImageDownloaderOptions)options
                                        progress:(SDWebImageDownloaderProgressBlock)progressBlock
                                       completed:(SDWebImageDownloaderCompletedBlock)completedBlock;