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:

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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:

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?

果然问题得以解决。

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