大量内存消耗:ImageIO_jpeg_Data [英] Massive Memory Consumption: ImageIO_jpeg_Data

问题描述

我有一个TableViewController，它显示用户图像和每行条目一些文本.该图像通过"cellForRowAtIndexPath"方法加载:

I've got a TableViewController that shows an user image and some text per row entry. This image is loaded in the "cellForRowAtIndexPath" method:

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    var cell : ApplicantsCell = tableView.dequeueReusableCellWithIdentifier("Cell") as! ApplicantsCell

    {...}

    let image = UIImage(named: "avatar")
    cell.applicantImage.image = image

    if let applImage = applicant.image as PFFile? {
        applImage.getDataInBackgroundWithBlock {
            (imageData: NSData?, error: NSError?) -> Void in
            if error == nil {
                let image = UIImage(data: imageData!)
                cell.applicantImage.image = image
            }
        }
    }
    return cell
}

每次我重新打开应用程序并转到此TableViewController时，Instruments都会向我显示，将创建一个新的"ImageIO_jpeg_Data"对象，而旧的对象将永远不会释放.每个对象大约需要13 MB的内存...因此，经过几次迭代，内存使用量超过了100 MB并继续...: 内存使用情况http://twail.net/stack/screen.png .

Every time I re-open the app and go to this TableViewController, Instruments shows me, that a new "ImageIO_jpeg_Data" object is created and the old ones get never released. Each of this objects takes about 13 MBs of memory... So after a few iterations, the memory usage passes 100 MB and goes on...: Memory Usage http://twail.net/stack/screen.png.

在模拟器中触发内存不足警告不会释放任何内存...

And triggering a low memory warning in the simulator does not free any memory...

有人可以帮我如何释放内存吗?

Can somebody help me how I can deallocate memory?

推荐答案

您做错了两件事.

首先，在将图像添加到单元格之前，请始终将图像缩小到实际的显示尺寸.仅在内存中保留13 MB的图像，以便您可以在单元格中显示该图像的缩略图版本是错误的.

First, always scale the image down to the actual display size before adding it to the cell. Keeping a 13 MB image in memory just so you can show a tiny thumbnail version of that image in a cell is just wrong.

第二，此代码毫无意义，会给您带来麻烦:

Second, this code makes no sense and will get you in trouble:

        if error == nil {
            let image = UIImage(data: imageData!)
            cell.applicantImage.image = image
        }

请记住，单元格已被重用，因此在运行此代码时，cell指向的单元格可能不再存在于接口中，或可能显示表的另一行(因为已被重用) .而是将(按比例缩小的)图像存储在数据模型中，然后重新加载表.

Remember, the cells are reused, so by the time this code runs, the cell pointed to by cell may no longer exist in the interface, or may be showing a different row of the table (because it was reused). Instead, store the (scaled-down) image in the data model and reload the table.

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