App crashes when trying to copy text on iPhone - ios

Question

I program an "encryption app" that encrypts texts in a simple way. This is the code:
let smallLetters: String = "abcdefghijklmnopqrstuvwxyz"
let bigLetters: String = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
let input: String = encryptTextField.text!
encryptTextField.text! = ""
var value: String = ""
for c in input {
let otherChars: String = " !§$%&/()=?´`#+'*-_.:,;<>^°#€{}≠¿|][¢¶“¡≤≈ç√∫~µ#€öäüÜÖÄ"
for i in otherChars {
if c == i {
value += String(i)
print("i")
}
}
var dCount: Int = 0
var eCount: Int = 0
var dFound: Bool = false
var eFound: Bool = false
for d in smallLetters {
if !dFound {
if c == d {
dFound.toggle()
let y: Int = smallCount - dCount
var z: Int = 1
for i in smallLetters {
if y == z {
print("[\(c) -> \(i)]")
value += String(i)
}
z += 1
}
} else {
dCount += 1
}
}
}
for e in bigLetters {
if !eFound {
if c == e {
eFound.toggle()
let y: Int = bigCount - eCount
var z: Int = 1
for i in bigLetters {
if y == z {
print("[\(c) -> \(i)]")
value += String(i)
}
z += 1
}
} else {
eCount += 1
}
}
}
}
let maximumChars: Int = 15
var string: String = ""
var i: Int = 1
var b: Bool = false
for c in value {
if !b {
if i <= maximumChars {
string += String(c)
} else {
string += "..."
b = true
}
i += 1
}
}
let alert: UIAlertController = UIAlertController(title: "Encoded!", message: "Your input is now encrypted / decrypted.", preferredStyle: UIAlertController.Style.alert)
let cancel: UIAlertAction = UIAlertAction(title: "OK", style: UIAlertAction.Style.cancel, handler: { (alert: UIAlertAction!) in
self.encryptTextField.text! = value
print("OK")
self.encryptTextField.placeholder = "Enter a text to encrypt..."
})
let copy: UIAlertAction = UIAlertAction(title: "Copy!", style: UIAlertAction.Style.default, handler: { (alert: UIAlertAction!) in
print("Copy!")
let pasteboard: UIPasteboard = UIPasteboard.general
pasteboard.string! = value
self.encryptTextField.placeholder = "'" + string + "' was copied!"
})
alert.addAction(cancel)
alert.addAction(copy)
present(alert, animated: true, completion: nil)
So that I can quickly insert the encrypted text into another app (e.g. WhatsApp) I use this code (simplified):
let pasteboard: UIPasteboard = UIPasteboard.general
pasteboard.string! = "Hello World!"
The code works in the simulator: The encrypted text is copied and I can paste it with a double click (see picture).
Paste encrypted text with a double click
But when I run the app on my mobile phone (iPhone 8), the app crashes at this point!
Does anyone know a solution or at least know why?

Answer 1

The solution here is to not force unwrap optional variables in your code.
I highly recommend to read more about Optionals in Swift here.
let input: String = encryptTextField.text!
The text in a UITextField can be nil. The data type is a String optional(String?)
Instead of the above, use if let statements to safely unwrap optionals!
if let input = encryptTextField.text{
// Your logic/code to process input as String goes here
}
Similarly, You can remove the force unwrapping("!") done here.
1. encryptTextField.text! = "". Just use encryptTextField.text = ""
2. pasteboard.string! = value You can remove the force unwrapping("!") done here.
3. pasteboard.string! = "Hello World!"
Basically only force unwrap variables if you for sure know that the value that the optional variable holds is not nil!
Force unwrapping optional variables that hold a nil value will crash you app!