How do I use the return value of a sheet to decide whether or not to close a window?

I want to use windowShouldClose: in my NSWindowController subclass to pop up a sheet asking if the user wants to save changes before closing with Save, Cancel, and Don't Save buttons.

The issue I'm running in to is that beginSheetModalForWindow:... uses a delegate instead of a return value.

I can return NO in windowShouldClose:, but then when I send [self close] to the controller in the panel's delegate nothing happens.

Can somebody explain to me how to do this or point me in the direction of some sample code?

The basic solution is to put a boolean flag on the window that states whether or not the window has warned about unsaved changes. Before calling [self close], set this flag to true.

Finally, in the windowShouldClose method, return the value of the flag.