How to change a variable to use outside of its scope in a if statement?

I have three global variables:

var activeTextField = UITextField() // stores the last textFieldDidBeginEditing
var activeTextView = UITextView() // stores the last textViewDidBeginEditing
var lastTextKindIsTextView = true // indicates if the last text used is a UITextView

I would like to count the number of selected characters of the first responder text field or text view. I tryed with this code but it don't work because activeField is out of scope. Is there a way to do this?

if lastTextKindIsTextView {
    let activeField = activeTextView
} else {
    let activeField = activeTextField
}

// see the length of the selected string
var strLength = 0

// don't work because activeField is out of scope:
if let textRange = activeField.selectedTextRange { 
    let selectedText = activeField.text(in: textRange)
    strLength = (selectedText?.utf16.count)!
 }