How to handle Cocoa application termination properly?

Question

So, here's my case :

I'm developing a NON-standard document-based application and I want to handle the scenario of aborting the termination when there still are unsaved changes in any of the documents.

My initial idea is :

• User tries to quit the application (either through the "Quit XXXXX" menu item or by clicking the "X" button)
• Are there any modified documents?
• if NO : quit
• if YES : notify user that there are unmodified documents. if he wants to proceed, then quit. Else cancel termination.

So, I decided to do it the delegate-way.

In my Application delegate, I've implemented :

• -windowToClose: (triggered on NSWindowWillCloseNotification)
• applicationShouldTerminate:
• applicationShouldTerminateAfterLastWindowClosed:

Now, that's what I'm thinking. In the applicationShouldTerminate: method :

• Return NSTerminateNow if no modified documents exist
• Return NSTerminateCancel if there ARE modified documents. In that case, pop up an alert sheet or something like that and if user confirms he wants to quit, then call a [NSApp terminate:nil];

Is that the right way to go about it?

Any suggestions?

Answer 1

That's indeed how to do it. But in your applicationShouldTerminate implementation, you should just pop up the alert right there, and return NSTerminateNow if the user didn't click Cancel; NSTerminateCancel otherwise. No need to manually terminate the application later.

Edit: to show an alert as a sheet but run it as a modal dialog, call beginSheetModalForWindow on the alert, then call [NSApp runModalForWindow:alert]. In addition, in the end selector that you pass for beginSheetModalForWindow, you need to call [NSApp stopModal] to get out of the modal loop.

However, it is better in this case to run the alert as a sheet for the window, and return NSTerminateLater in your applicationShouldTerminate implementation. Then, in the end selector for the alert, call [NSApp replyToApplicationShouldTerminate:]. This is how Apple recommends you implement this.