Swift: Copy/paste enable and disable for specific fields

Question

I have create username and create password. There is no character limit for username but password is has 8 digit character limit. How to disable the copy/paste only for password field. And also how to filter some characters which are not valid for username.

Answer 1

For the Copy and Paste Question:

You will need to create your own TextField class that inherits UITextField and then override the canPerformAction delegate method to disable pasting:

override func canPerformAction(action: Selector, withSender sender: AnyObject?) -> Bool {
    if action == "paste:" {
        return false
    }        
    return super.canPerformAction(action, withSender: sender)
}

More detailed description: How to disable Pasting in a TextField in Swift?

For the Characters Question:

Similar concept as above, except you will need to implement the textFieldDidEndEditing or shouldChangeCharactersIn delegate methods.

textFieldDidEndEditing will allow you to evaluate the string in the field AFTER the user has stopped editing that field. Example:

func textFieldDidEndEditing(_ textField: UITextField, reason: UITextFieldDidEndEditingReason) {
    switch textField {
        case usernameTextField:
            // evaluate the `textField.text` for is a valid username
        case passwordTextField:
            // evaluate the `textField.text ` for is a valid password
    }
}

shouldChangeCharactersIn will allow you to evaluate the string for every keystroke (I prefer using the later when evaluating textfield inputs). Example:

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {

    switch textField {
        case usernameTextField:
            // evaluate the `replacementString` for is a valid username
        case passwordTextField:
            // evaluate the `replacementString` for is a valid password
    }
    return true
}