Problems with unwinding a segue

Question

Having a real issue with this.

I have now managed to transfer my label data across a segue and display it on a new view controller. Thank you to all of those who helped with this. For this I used the following code:

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    let BMI_Result = segue.destination as! BMI_Result
    
    if let text = result3Label.text {
        BMI_Result.text = text
    }

The problem I am having now is that when I try to unwind segue using a back button from this view, the app crashes and I get the following error:

• Thread 1: signal SIGABRT

The as! command in the code has a red underline.

I have read up on the signal SIGABRT error and from what I can see, it's a generic error for that line of code. I presume it is because this code is linked to another segue but I don't know how to correct it.

Anyone got any ideas?

I have attempted to redo the back segue and link the button to the contents page. None of this has worked.

Answer 1

The issue here is the force cast as!. As you go back your destination has changed.

Change this to an optional cast and guard against it.

guard let BMI_Result = segue.destination as? BMI_Result else{
    return
}

if let text = result3Label.text {
    BMI_Result.text = text
}