ios - 在 dispatch_async 中收到内存警告

Question

这是我在 cellForRowAtIndex 中编写的用于下载图像的代码:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

    @autoreleasepool {
        __block UIImage * img;
        __block NSData *data;
        if(![messageDocument.SmallImageURL isEqual:@""])
        {
            data = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:messageDocument.SmallImageURL]];
            img = [UIImage imageWithData:data];
        }

        dispatch_async(dispatch_get_main_queue(), ^{
            imgUser.image = img;
            img = nil;

            imgUser.contentMode = UIViewContentModeScaleAspectFill;
            CGSize size;
            if(imgUser.image.size.width > imageFrame.size.width || imgUser.image.size.height > rectImage.size.height)
            {
                if(imgUser.image.size.width < imageFrame.size.width)
                {
                    rectImage.size.width = imgUser.image.size.width;
                }

                if(imgUser.image.size.height < rectImage.size.height)
                {
                    rectImage.size.height = imgUser.image.size.height;
                }

                size = CGSizeAspectFit(imgUser.image.size, rectImage.size);
                imgUser.frame = CGRectMake(imgUser.frame.origin.x, rectImage.origin.y, size.width, size.height);

                height = imgUser.frame.size.height;
            }
            else
            {
                imgUser.frame = CGRectMake(imageFrame.origin.x, imageFrame.origin.y, imgUser.image.size.width, imgUser.image.size.height);
                height = imgUser.image.size.height;

            }

            CGPoint contentOffset = tableMessageDetail.contentOffset;
            [tableMessageDetail beginUpdates];
            [tableMessageDetail endUpdates];
            [tableMessageDetail setContentOffset:contentOffset];
        });

            messageDocument.Pic = data;
            data = nil;
        if(messageDocument.Pic != nil)
        {
            Attachment *attachment = [Attachment new];
            attachment.DocId = messageDocument.DocId;
            attachment.DocURL = messageDocument.DocURL;
            attachment.ImageId = messageDocument.ImageId;
            attachment.MessageId = messageDocument.MessageId;
            attachment.SmallImageURL = messageDocument.SmallImageURL;
            attachment.OriginalFileName = messageDocument.OriginalFileName;
            if([messageDocument.DocURL isEqual:@""])
            {
                NSArray *attachmentArray = [messageDocument.SmallImageURL componentsSeparatedByString:@"/"];
                NSString *attachmentName = [attachmentArray objectAtIndex:attachmentArray.count - 1];
                attachment.AttachmentName = attachmentName;
            }
            else
            {
                NSArray *attachmentArray = [messageDocument.DocURL componentsSeparatedByString:@"/"];
                NSString *attachmentName = [attachmentArray objectAtIndex:attachmentArray.count - 1];
                attachment.AttachmentName = attachmentName;
            }

            attachment.Pic = messageDocument.Pic;
            [[CommonModel shared]CreateAttachment:attachment];
            [[CommonModel shared]UpdateMessageDocumentPic:messageDocument];

            attachment = nil;
        }
    }
});  

但是如果有超过 6 张图片，我会在控制台上收到内存异常并显示以下消息:

Message from debugger: Terminated due to memory issue

Answer 1

你的下载逻辑没有问题。问题是您试图将图像保存在阵列中，这最终会增加您的应用程序内存。由于您持有的图像是压缩的 png，它们似乎没有太大的尺寸，但它会大大增加您的应用程序的内存并可能使您的应用程序崩溃。

要解决您的问题，您需要在下载每个文件后立即将其保存到文档目录，然后保存图像的名称(如果需要在某处显示，则保存缩略图)而不是整个完整分辨率图片。

更新

您可以使用 Xcode 中的 instruments 工具分析应用程序的内存分配。它可以为您提供消耗最多内存的对象的提示。