What's the correct way to capture the return code of an alert sheet for OS X 10.9+?

Question

According to Apple's documentation, it appears that the only non-deprecated method for displaying an alert sheet is beginSheetModalForWindow:completionHandler:, where completionHandler block takes an argument of NSModalResponse-type. NSModalResponse is an enum with only 3 possible values: NSModalResponseStop, NSModalResponseAbort and NSModalResponseContinue. So how do I know which button on an alert sheet was clicked by the user?

Answer 1

The result code is not really an enum in the sense that it's not restricted to just the values of the NSModalResponse type. The enum is only used to define some of the possible values.

See the documentation for the -addButtonWithTitle: method of NSAlert, for example, which explains the response codes generated from the added button: NSAlertFirstButtonReturn for the first, NSAlertSecondButtonReturn for the second, NSAlertThirdButtonReturn for the third, and NSAlertThirdButtonReturn + n for subsequent buttons.

See also the documentation for the -runModal method:

If you use alertWithMessageText:defaultButton:alternateButton:otherButton:informativeTextWithFormat: to create an alert, the following constants are used to identify the button used to dismiss the alert: NSAlertDefaultReturn, NSAlertAlternateReturn, and NSAlertOtherReturn. Otherwise, the constants used are the ones described in “Button Return Values.”

That's the same rule that applies for the response code passed to the completion handler you supply to -beginSheetModalForWindow:completionHandler:.