解决MWPhotoBrowser中的SDWebImage加载大图导致的内存警告问题

iOS开发 · 2015-01-22 11:31

解决MWPhotoBrowser中的SDWebImage加载大图导致的内存警告问题_第1张图片

MWPhotoBrowser是一个非常不错的照片浏览器,在github的star接近3000个,地址:https://github.com/mwaterfall/MWPhotoBrowser.git


MWPhotoBrowser来加载小图1M以下的都应该不会有内存警告的问题。如果遇到大图,3M、4M、5M的大图,很有可能导致内存警告。最近我就遇到这个问题,很是头疼。来回滑动查看照片内存飙到100M以上:


解决MWPhotoBrowser中的SDWebImage加载大图导致的内存警告问题_第2张图片


网上查了很多资料,都没有解决问题。


我们来看一下MWPhotoBrowser,其实MWPhotoBrowser用的是SDWebImage来下载图片的。地址:https://github.com/rs/SDWebImage.git


在github看到SDWebImage的介绍,后面说到:

Future Enhancements

  • LRU memory cache cleanup instead of reset on memory warning


看到这个真是欲哭无泪啊。


再去看看SDWebImage的,有个人提问了:


How to disable "memory cache"? I don't want memory cache, it used a lot of memory and got memory waring easily, disk is enough for me...


有人回答:


There is no way to disable the memory cache. But the cache is designed to flush itself when you get a memory warning, so you shouldn't need to worry it.



说的是SDWebImage遇到内存警告会自动释放内存,但是这还是解决不了问题,加载大图的时候,内存会突然蹦到100多M,在4s及以下的手机上跑,再就挂了。


还是没有解决内存警告的问题。怎么办呢?


我是这么解决的:


SDWebImage有一个SDWebImageDownloaderOperation类来执行下载操作的。里面有个下载完成的方法:



- (void)connectionDidFinishLoading:(NSURLConnection *)aConnection {
SDWebImageDownloaderCompletedBlock completionBlock = self.completedBlock;
@synchronized(self) {
CFRunLoopStop(CFRunLoopGetCurrent());
self.thread = nil;
self.connection = nil;
[[NSNotificationCenter defaultCenter] postNotificationName:SDWebImageDownloadStopNotification object:nil];
}

if (![[NSURLCache sharedURLCache] cachedResponseForRequest:_request]) {
responseFromCached = NO;
}

if (completionBlock)
{
if (self.options & SDWebImageDownloaderIgnoreCachedResponse && responseFromCached) {
completionBlock(nil, nil, nil, YES);
}
else {
UIImage *image = [UIImage sd_imageWithData:self.imageData];
NSString *key = [[SDWebImageManager sharedManager] cacheKeyForURL:self.request.URL];
image = [self scaledImageForKey:key image:image];

// Do not force decoding animated GIFs
if (!image.images) {
image = [UIImage decodedImageWithImage:image];
}
if (CGSizeEqualToSize(image.size, CGSizeZero)) {
completionBlock(nil, nil, [NSError errorWithDomain:@"SDWebImageErrorDomain" code:0 userInfo:@{NSLocalizedDescriptionKey : @"Downloaded image has 0 pixels"}], YES);
}
else {
completionBlock(image, self.imageData, nil, YES);
}
}
}
self.completionBlock = nil;
[self done];
}


其中,UIImage *image = [UIImage sd_imageWithData:self.imageData];就是将data转换成image。


再看看sd_imageWithData:这个方法:


+ (UIImage *)sd_imageWithData:(NSData *)data {
UIImage *image;
NSString *imageContentType = [NSData sd_contentTypeForImageData:data];
if ([imageContentType isEqualToString:@"image/gif"]) {
image = [UIImage sd_animatedGIFWithData:data];
}
#ifdef SD_WEBP
else if ([imageContentType isEqualToString:@"image/webp"])
{
image = [UIImage sd_imageWithWebPData:data];
}
#endif
else {
image = [[UIImage alloc] initWithData:data];
UIImageOrientation orientation = [self sd_imageOrientationFromImageData:data];
if (orientation != UIImageOrientationUp) {
image = [UIImage imageWithCGImage:image.CGImage
scale:image.scale
orientation:orientation];
}
}


return image;
}


这个方法在UIImage+MultiFormat里面,是UIImage的一个类别处理。这句话很重要image = [[UIImage alloc] initWithData:data]; SDWebImage把下载下来的data直接转成image,然后没做等比缩放直接存起来使用。所以,我们只需要在这边做处理即可:


UIImage+MultiFormat添加一个方法:


+(UIImage *)compressImageWith:(UIImage *)image
{
float imageWidth = image.size.width;
float imageHeight = image.size.height;
float width = 640;
float height = image.size.height/(image.size.width/width);

float widthScale = imageWidth /width;
float heightScale = imageHeight /height;

// 创建一个bitmap的context
// 并把它设置成为当前正在使用的context
UIGraphicsBeginImageContext(CGSizeMake(width, height));

if (widthScale > heightScale) {
[image drawInRect:CGRectMake(0, 0, imageWidth /heightScale , height)];
}
else {
[image drawInRect:CGRectMake(0, 0, width , imageHeight /widthScale)];
}

// 从当前context中创建一个改变大小后的图片
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
// 使当前的context出堆栈
UIGraphicsEndImageContext();

return newImage;

}


然后在:image = [[UIImage alloc] initWithData:data];下面调用以下:


if (data.length/1024 > 1024) {
image = [self compressImageWith:image];
}


当data大于1M的时候做压缩处理。革命尚未成功,还需要一步处理。在SDWebImageDownloaderOperation的connectionDidFinishLoading方法里面的:


UIImage *image = [UIImage sd_imageWithData:self.imageData];

//将等比压缩过的image在赋在转成data赋给self.imageData
NSData *data = UIImageJPEGRepresentation(image, 1);
self.imageData = [NSMutableData dataWithData:data];


大工告成,我们来看一下效果吧:


解决MWPhotoBrowser中的SDWebImage加载大图导致的内存警告问题_第3张图片


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