How to set save notification when click close in document based application

I am doing a simple document based application. I've implemented readFromData and dataOfType function. Creating a newDocument and saveDocument are working. However, the question is how to set up save notification when user clicks Close. I add some data in my application and when I click close, it just directly close. There is no save notification. I think it was supposed to have it in document based application.

I tried windowWillClose:(NSNotification*)a, having an alertsheet. The alert comes and window closes immediately.

What I am missing?

Solution

Implement this kind of logic, and you will be done.

- (BOOL)isDocumentEdited{
        if (somethingGotChanged){
            return YES;
        }
        else{
            return NO;
        }
        //or return somethingGotChanged; //*** make somethingGotChanged BOOL
    }

Here, somethingGotChanged is a flag, which you have to set based on you editing on the data.