取消要求Alamofire图片的请求

Question

Basic Information: I have a tableView and each tableView cell containing an image and few labels . I use tableView prefetch data method to make API calls to fetch data as the tableView scrolls.

Issue: Sometimes I see a particular cell showing an image of some other cell . This happens when I scroll a little faster than normal speed. Note: In order to overcome from this issue I just need to scroll the tableView up/down

Things tried: I have set the imageView to nil in prepare for reuse method.

The conclusion I have reached: By debugging the issue I understood that once a cell is visible I make an image request using Alamofire Image but I scroll it before we received the response. So, what might be happening is that on receiving a response it is setting an image for the cell but that cell is not visible as I am reusing the cells. The cell contains some other data.

Please let me know how can I cancel the request if the cell is not visible. Let me know if I am missing something in the question.

Answer 1

This is happening because tableView reuse the cells and if it having a image downloading in queue and you scroll and the downloading is complete, it shows the downloaded image for few second until correct image download.

use placeholder in af_setImage method. it will solve your problem

imageView.af_setImage(withURL: URL(string: img)!, placeholderImage: UIImage(named: "product_placeholder")

Answer 2

What I do in this situation is set the cell's tag to match the row number.

When the image requests complete, I check if it still has the same tag (if it was reused, tag would be changed).

Something like this, in cellForRowAt indexPath :

cell.tag = indexPath.row
ImageService.shared.getImage(completion: { (image) in
  if let image = image, cell.tag == indexPath.row {
    //apply image
  }
}

This doesn't cancel the request, but it ignores the result if the cell is not in the same position anymore.