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

作者:  发布日期:2015-01-22 22:07:05
Tag标签:内存  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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