Overriding UINav Controller back button

Do you know of any application that does anything like you want?

I can.

Mail.

Compose, type, cancel. It presents an alert at the bottom of the screen.

How does it work?

Compose is presented modally. Thus it doesn't have a default back button. Instead, it has a cancel button. You have to program cancel buttons yourself in a modal view. Thus you can make it so when the cancel button is pushed, it presents a warning before calling to its delegate that it's time for it to be dismissed.

Another example is Contact -> new -> cancel.

 

I'm not certain of this as I haven't used a modal view in nearly a year, but I think the best way to do this is going to be more along the lines of:

Make a new .xib file. Drop in a nav bar. Drop in a cancel button. Hook up the cancel button to a cancel IBAction. In that, check if the data has been changed, and if it has been, pop up that warning (I forget what the warning that pops up from the bottom of the screen is called. Maybe a UIActionSheet or something like that?) If it hasn't been, just tell the delegate to dismiss. If the user tells the warning they don't care, tell the delegate to dismiss. If the user tells the warning they do care, then dismiss the warning and don't tell the delegate anything.

The delegate controls when the modal view appears / disappears. The view's controller just requests to be dismissed by the delegate. Why? I can't actually remember why... I remember one of the Stanford lectures covered it a few years ago.