解决MWPhotoBrowser中的SDWebImage加载大图导致的内存警告问题
MWPhotoBrowser是一个非常不错的照片浏览器,在github的star接近3000个,<a href="https://github.com/mwaterfall/MWPhotoBrowser.git"target="_blank"title="进入官网">MWPhotoBrowser下载</a>
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:
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。<a href=" https://github.com/rs/SDWebImage.git"target="_blank"title="进入官网">SDWebImage下载</a>
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:
?
果然问题得以解决。
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