Why swift GCD not work in tableview cell imageView - ios

Question

I made a chat app. When I chatting and post image message to A man. I check my image upload successful,and download to local document failed. A man's view just have imageView with clear background.No image to show,and I click back to previous view,then go back chat view. The image show up. what's happen? how to let image download to local immediatly? Thanks!!
This is my download function code:
func ImageFromUrl(imageView:UIImageView,url:String) {
let documentsDirectoryURL = try! FileManager().url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: true).appendingPathComponent("\(Image)/")
let fileName = url + ".jpg"
let fileURL = documentsDirectoryURL.appendingPathComponent(fileName)
let urlString = URL(string: url)
if let image = UIImage(contentsOfFile: fileURL.path)
{
imageView.image = image
return
}
DispatchQueue.global().async {
let data = try? Data(contentsOf: urlString!) //make sure your image in this url does exist, otherwise unwrap in a if let check / try-catch
if data != nil
{
if let image = UIImage(data: data!)
{
if !FileManager.default.fileExists(atPath: fileURL.path) {
if let jpegData = UIImageJPEGRepresentation(image, 0.001)
{
do {
try jpegData.write(to: fileURL, options: .atomic)
} catch {
debug(object: error)
}
}
} else {
debug(object:"file already exists")
}
DispatchQueue.main.async {
imageView.image = image//UIImage(data: data!)
}
}
}
}
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell: CustomTableViewCell = CustomTableViewCell(style: .default, reuseIdentifier: nil)
if cell.isRight == false { //A man's cell View
ImageFromUrl(imageView:cell.imageView,url:imageUrl)
//tableView.reloadRow(at:indexPath, with: .automatic)
//tableView.reloadRows(at: [indexPath], with: .automatic)
//tableView.reloadRow(UInt(contents.count-1), inSection: 0, with: .automatic)
}
}

Answer 1

Since this is being pushed to GCD the table will finish updating while the image is loaded. Therefore you will need reload the data in the table view.
Change:
DispatchQueue.main.async {
imageView.image = image//UIImage(data: data!)
}
to:
DispatchQueue.main.async {
imageView.image = image//UIImage(data: data!)
self.tableView?.reloadData()
}
But this won't be enough, as the image will be recreated each time tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell is called and you will be caught in an infinite loop. I would recommend subclassing UITableViewCell to create your own cell that contains an image property. Then you can tell ImageFromURL(_) to save the image to the cell's image property, and then reload the view.