无法将类型 '(_) throws -> ()' 的值转换为预期的参数类型 '((UIAlertAction) -> Void)?'

Question

First of all, thank you so much for helping me. I do not understand this error and am unable to find a solution.

I have looked at other answers but they didn't seem to help. Here is my code. The error shows up on the let action line.

  @IBAction func addButtonPressed(_ sender: UIBarButtonItem) {

    var textField = UITextField()

    let alert = UIAlertController(title: "Add New Todoey Item", message: "", preferredStyle: .alert)


    let action = UIAlertAction(title: "Add item", style: .default) { (UIAlertAction) in





        //what will happen once the user clicks the Add Item button on our UIAlert

        let newItem = item()
        newItem.title = textField.text!
        self.itemArray.append(newItem)

   let encoder = PropertyListEncoder()

        do {

        let data = try encoder.encode(self.itemArray)
        }

        catch {

            try Data.write(to: self.dataFilePath!)
            print("Error encoding item array, \(error)")

        }


        //reloads table view data
        self.tableView.reloadData()

      }

alert.addTextField { (alertTextField) in

        alertTextField.placeholder = "What Needs To Be Done?"
      textField = alertTextField
    }

alert.addAction(action)
  present(alert, animated: true, completion: nil)

}

Error: Cannot convert value of type '(_) throws -> ()' to expected argument type '((UIAlertAction) -> Void)?'

Answer 1

Three issues:

1. The parameter in the action must be an instance, not a type

   let action = UIAlertAction(title: "Add item", style: .default) { action in

   or if the action is unused

   let action = UIAlertAction(title: "Add item", style: .default) { _ in

2. Data.write(to:.. must be data.write(to:..

3. The third issue causes the (a bit misleading) error message: the data line must be inside the do block. The error indicates that there is no do block around the try statement

   do { let data = try encoder.encode(self.itemArray) try data.write(to: self.dataFilePath!) } catch { print("Error encoding item array, \\(error)") }