Display alert from custom cell in swift 3 - ios

Question

I have designed custom cells in listViewCell.swift and listViewCell.xib. In which i have textfield. When the user enters a number more than 100 then i want to show alert.
I have tableView in HomeViewController.
let alert = UIAlertController(
title: "Error",
message: "Please Insert value less than 100",
preferredStyle: UIAlertControllerStyle.alert
)
alert.addAction(UIAlertAction(
title: "Click",
style: UIAlertActionStyle.default,
handler: nil
))
UIApplication.shared.keyWindow?.rootViewController?.present(alert, animated: true, completion: nil)
then it gives me Attempt to present <UIAlertController: 0x7f945a5a67d0> on <ProjName.LoginController: 0x7f945a407e70> whose view is not in the window hierarchy!
and when i change the code to
let alert = UIAlertController(
title: "Error", message: "Please Insert value less than 100",
preferredStyle: UIAlertControllerStyle.alert
)
alert.addAction(UIAlertAction(
title: "Click",
style: UIAlertActionStyle.default,
handler: nil
))
HomeViewController().present(alert, animated: true, completion: nil)
then it gives me unexpectedly found nil while unwrapping an Optional value
and points to
override func viewDidLoad() {
super.viewDidLoad()
**tableViewList.delegate = self**
tableViewList.dataSource = self
searchBar.delegate = self
}
How can i show a alert from a custom cell? or how can we create a common alert function in HomeViewController and show it form any swift file?
Thanks in Advance

Answer 1

You could go with making delegates of your custom cell. Set the delegate of your custom cells, let's say didEnterInvalidValue didEnterValidValue, to your HomeViewController. From those delegate implementations, show your UIAlertController with custom messages.
Or you can iterate over your self.navigationController?.viewControllers to find the top view controller and show UIAlertController on that view controller's view.

Answer 2

Most easiest would be
Step 1:
From your View controller where you have used your custom Cell, make a common delegate function for your textField which purpose is to notify you about text length.
You may need to extend UITextFieldDelegate for this.
Or u can assign a target function to your textField(Not sure if it works though)
How do you catch Specific TextField?
You need to assign a tag for every textField using indexPath and catch that specific textField using that tag.
Step 2:
In that function you can show your alert by only using
self.present(alert, animated: true, completion: nil)

Answer 3

I would go for the delegate answer. But for a faster solution, at several projects I create a singleton from the rootViewController (generally the UINavigationController) at AppDelegate so it can get the rootController any time. Using keyWindow, it's not very recommended since the keyWindow it's not always the one controlled by who, for example, alert dialog redefine it.
Another projects I create a AlertClass singletone, where it's initialised by the rootController, and it's always invoked from it.