This question is relative to this thread: how-to-set-the-height-of-a-cell-depending-on-a-uilabel-with-a-typewriter-effect
In my tableViewController, my cell contains UILabel with a typewriter effect managed with setTextWithTypeAnimation;
func configureCell(tableView: UITableView, cell: ParagraphTableViewCell, atIndexPath indexPath: IndexPath) {
let paragraph = paragraphArray[indexPath.row] as! Paragraph
cell.paragraph = paragraph
self.queue = OperationQueue()
let operation1 = BlockOperation(block: {
cell.dialogueLabel.setTextWithTypeAnimation(typedText: paragraph.dialogueLabel.text!, queue:self.queue, callBackAfterCharacterInsertion: {
self.tableView.beginUpdates()
self.tableView.endUpdates()
})
})
operation1.completionBlock = {
cell.buttonsStackViewHeightConstraint.constant = CGFloat(HEIGHT_CONSTRAINT)
UIView.animate(withDuration: 0.3, animations: {
cell.contentView.layoutIfNeeded()
}, completion: nil)
}
queue.addOperation(operation1)
}
My typewriter is inside a UILabel extension :
extension UILabel {
func setTextWithTypeAnimation(typedText: String, queue: OperationQueue, characterInterval: TimeInterval = 0.05, callBackAfterCharacterInsertion:(()->())?) {
text = ""
for (_, character) in typedText.characters.enumerated() {
if queue.isSuspended {
OperationQueue.main.isSuspended = true
OperationQueue.main.cancelAllOperations()
break;
}
OperationQueue.main.addOperation {
self.text = self.text! + String(character)
callBackAfterCharacterInsertion?()
}
Thread.sleep(forTimeInterval: characterInterval)
}
}
}
First I used DispatchQueue to manage the animation inside a cell (see how-to-set-the-height-of-a-cell-depending-on-a-uilabel-with-a-typewriter-effect), but I needed to stop the thread when user closes the view controller. That's why I'm using OperationQueue (DispatchQueue cannot be stopped)
@IBAction func closeViewController(sender: AnyObject) {
dismiss(animated: true, completion: nil)
if self.queue != nil {
self.queue.isSuspended = true
self.queue.cancelAllOperations()
self.queue = nil
}
}
The issue is when completionBlock is called, the app crashes when I try to update a layout constraint.
This application is modifying the autolayout engine from a background thread after the engine was accessed from the main thread.
How can avoid this crash?
You must call UI stuff on the mainQueue.
Example:
operation1.completionBlock = {
DispatchQueue.main.async {
cell.buttonsStackViewHeightConstraint.constant = CGFloat(HEIGHT_CONSTRAINT)
UIView.animate(withDuration: 0.3, animations: {
cell.contentView.layoutIfNeeded()
}, completion: nil)
}
}