ios – 在UITableView中显示大图像的内存问题

我有一个系统从Web上加载很多大图像并将它们显示在自定义表格单元格中.在较旧的设备上,内存警告发生得非常快,所以我实现了一个从表中删除一些系统以试图解决这个问题的系统,但它不能很好地工作(很多图像被删除影响了UI).

所以我想我可以将所有图像加载到设备的缓存中,然后从那里加载它们 – 我已经实现了SDWebImage.这很好但我仍然没有解决内存分配的问题,因为图像仍然一直在显示因此留在记忆中 – 导致崩溃.

我想我需要实现一个系统,显示图像(来自缓存),如果单元格正在显示,如果单元格没有显示则隐藏它 – 我只是坚持如何构建这样的系统.

或者这不起作用？你真的可以通过从表格单元中删除图像来保持应用程序内存不足(并停止内存警告/崩溃)吗？或者我只需要继续使用我之前的解决方案并删除图像/单元格直到内存警告停止？

更新了代码

TableViewController.m

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath 
{   
    if (indexPath.section == 0)
    {
    currentIndexPath = indexPath;

    ImageTableCell *cell = (ImageTableCell *)[tableView dequeueReusableCellWithIdentifier:CellIdentifier];

    ImageDownloader *download = [totalDownloads objectAtIndex:[indexPath row]];

    if (cell == nil) 
    {
        cell = [[[ImageTableCell alloc] initWithStyle: UITableViewCellStyleDefault reuseIdentifier: CellIdentifier] autorelease];
    }

    cell.imageView.image = download.image;

    return cell;
}
return nil;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section 
{   
    int t = [totalDownloads count];   
    return t;
}

ImageTableCell.m – 自定义单元格

- (id)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(NSString *)reuseIdentifier
{
self = [super initWithStyle:style reuseIdentifier:reuseIdentifier];
if (self) 
{
    self.frame = CGRectMake(0.0f,0.0f,320.0f,0.0f);
    self.contentView.frame = CGRectMake(0.0f,0.0f);

    self.autoresizingMask = (UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth);
    self.contentMode = UIViewContentModeScaleToFill;
    self.autoresizesSubviews = YES;

    self.contentView.autoresizingMask = (UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth);
    self.contentView.contentMode = UIViewContentModeScaleToFill;
    self.contentView.autoresizesSubviews = YES;

    [self.imageView drawRect:CGRectMake(0.0f,0.0f)];
    self.imageView.contentMode = UIViewContentModeScaleAspectFill;
    self.imageView.autoresizingMask = (UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth);
    self.imageView.opaque = YES;
}
return self;
}

ImageDownloader(实现SDWebImageManagerDelegate)

-(void) downloadImage // Comes from Model class
    {    
    if (image == nil)
    {
        NSURL *url = [NSURL URLWithString:self.urlString];

        SDWebImageManager *manager = [SDWebImageManager sharedManager];

        // Remove in progress downloader from queue
        [manager cancelForDelegate:self];

        if (url)
        {   
            [manager downloadWithURL:url delegate:self retryFailed:YES];
        }
    }
    }

    - (void)cancelCurrentImageLoad
    {
        [[SDWebImageManager sharedManager] cancelForDelegate:self];
    }

    - (void)webImageManager:(SDWebImageManager *)imageManager didFinishWithImage:(UIImage *)_image
    {      
        self.image = _image;

        if ([self.delegate respondsToSelector:@selector(addImageToModel:)]) [self.delegate addImageToModel:self];
    }
    - (void)webImageManager:(SDWebImageManager *)imageManager didFailWithError:(NSError *)error;
    {
        if ([self.delegate respondsToSelector:@selector(badImage)]) [self.delegate badImage];
    }

解决方法

下载图像后,请勿将大图像保留在内存中.只需创建一个小尺寸的图像(缩略图)即可在tableview中显示,并将较大的图像写入某个目录.

您可以使用以下代码创建图像的缩略图.

CGSize size = CGSizeMake(32,32);
            UIGraphicsBeginImageContext(size);
            [yourImage drawInRect:CGRectMake(0,32,32)];
            yourImage = UIGraphicsGetImageFromCurrentImageContext();
            UIGraphicsEndImageContext();

ios – 在UITableView中显示大图像的内存问题

解决方法

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