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Question

I am using below code to download image from server. This code is written under UserCell class, which is a subclass of UITableViewCell .

class UserCell: UITableViewCell {
    @IBOutlet weak var profileImage: UIImageView!

    override func awakeFromNib() {
        super.awakeFromNib()
        //calling related methods
    }

    /*
    * Other stuffs *
    */

   func refreshImage(fileURL: NSURL?) {
        unowned let unownedSelf = self
        DownloadManager.download(fileURL: imageURL!, completion: {(filePath) -> (Void) in
           dispatch_async(dispatch_get_main_queue(), { () -> Void in
           unownedSelf.profileImage.image = UIImage(contentsOfFile: filePath.path!)
           })
         }, error: { (error) -> (Void) in
            // Handle error        
       })
   }
}

UITableView Datasource implementation

class Friends: UIViewController {
    /*
    * Other stuffs *
    */

    func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
        let reusableIdentifier = "identifier"
        let userObject = arrUsers[indexPath.row] //arrUsers is my array of users
        let cell = tableView.dequeueReusableCellWithIdentifier(reusableIdentifier, forIndexPath: indexPath) as! UserCell
        cell.refreshImage(userObject.image)
        return cell
    }
}

But it crash with _swift_abortRetainUnowned error. To prevent the crash I used [weak self] and self?. But now the problem is self is not being released.

DownloadManager.download(fileURL: imageURL!, completion: { [weak self] (filePath) -> (Void) in
   dispatch_async(dispatch_get_main_queue(), { () -> Void in
       // culprit statement
       self?.profileImage.image = UIImage(contentsOfFile: filePath.path!)
      })
   }, error: { (error) -> (Void) in
        // Handle error        
})

If I comment out the culprit statement then my memory consumption is around 40Mb but with that statement it goes 200Mb+ and with the scroll it increased.

I am not able to understand what to do or what point I missed. Can anybody please help me to understand and solve this problem.

Answer 1

unowned and weak should not be used in your case. This closure does not create a reference cycle.

Obviously, when you use unowned you get the _swift_abortRetainUnowned because self becomes nil .

Since the goal is to update the cell with downloaded image, self (the cell) should be kept alive. Thus a strong reference to self should be used. self will be released by the closure as soon as it finishes.