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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,MWPhotoBrowser下载

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。SDWebImage下载

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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