I am following a tutorial online regarding a TableView Cell swipe action.
I can explain to myself every line, except completionHandler(true)
This is the code snippet
override func tableView(_ tableView: UITableView, trailingSwipeActionsConfigurationForRowAt indexPath: IndexPath) -> UISwipeActionsConfiguration? {
let deleteAction = UIContextualAction(style: .destructive, title: "Delete") { (action, sourceView, completionHandler) in
//Delete
self.restaurantNames.remove(at: indexPath.row)
self.restaurantLocations.remove(at: indexPath.row)
self.restaurantTypes.remove(at: indexPath.row)
self.restaurantIsVisited.remove(at: indexPath.row)
self.restaurantImages.remove(at: indexPath.row)
self.tableView.deleteRows(at: [indexPath], with: .fade)
// Call completion handler to dismiss the action button
completionHandler(true)
}
let shareAction = UIContextualAction(style: .normal, title: "Share") { (action, sourceView, completionHandler) in
let defaultText = "Just checking in at" + self.restaurantNames[indexPath.row]
let activityController = UIActivityViewController(activityItems: [defaultText], applicationActivities: nil)
self.present(activityController, animated: true, completion: nil)
// Call completion handler to dismiss the action button
completionHandler(true)
}
let swipeConfiguration = UISwipeActionsConfiguration(actions: [deleteAction, shareAction])
return swipeConfiguration
}
I don't quite understand what does this mean? Thanks in advance
All of the existing answers just paste Apple's documentation which answers precisely nothing. It says when it should be called but nothing about what it does to the UI.
As far as I can tell, calling completionHandler with either value will collapse the buttons. You can see this in action by calling the completion handler in a dispatch_after block with a delay. Specifying true vs. false makes no difference in my tests.
I have a feeling that I'm missing something, but Apple's documentation is opaque here.
Explanation: You call the completion handler with true to indicate you performed the action or false if you could not for some reason.
Check below demo code work:
func contextualToggleFlagAction(forRowAtIndexPath indexPath: IndexPath) -> UIContextualAction {
var email = data[indexPath.row]
let action = UIContextualAction(style: .normal,
title: "Flag") { (contextAction: UIContextualAction, sourceView: UIView, completionHandler: (Bool) -> Void) in
if email.toggleFlaggedFlag() {
self.data[indexPath.row] = email
self.tableView.reloadRows(at: [indexPath], with: .none)
completionHandler(true) // your task is successfully done.
} else {
completionHandler(false) // With some reason you unable to perform task so now you returning false.
}
}
action.image = UIImage(named: "flag")
action.backgroundColor = email.isFlagged ? UIColor.gray : UIColor.orange
return action
}
Third parameter of the UIContextualAction handler is a closure that tells UIContextualAction whether or not you performed the action. By calling completionHanlder(true) you're notifying UIContextualAction that you performed the requested action. If, for example, there was an error in your handler that precluded you from performing the desired action, you can notify the handler by calling completionHandler(false).
Documentation: https://developer.apple.com/documentation/uikit/uicontextualaction/handler