Objective-C passing around … nil terminated argument lists

Question

Having some issues with the ... in ObjectiveC.

I\'m basically wrapping a method and want to accept a nil terminated list and directly pass

Answer 1

This is specific to the OP's UIAlertView-wrapping case, and tested only on iOS7: It appears that once a UIAlertView has been initialised with otherButtons:nil, and then has its style set to UIAlertViewStylePlainTextInput it doesn't call its delegate's alertViewShouldEnableFirstOtherButton: to validate input. I'm not sure if this is a bug or intended behaviour but it broke my principle of least astonishment. This is reproducible with the following (I'll assume the delegate's alertViewShouldEnableFirstOtherButton: is implemented):

UIAlertView *av = [[UIAlertView alloc] initWithTitle:@"Title" 
                                             message:@"message" 
                                            delegate:self         
                                   cancelButtonTitle:@"Cancel" 
                                   otherButtonTitles:nil];
[av setAlertViewStyle:UIAlertViewStylePlainTextInput];
[av addButtonWithTitle:@"OK"];
[av show];

The solution, since UIAlertView happily accepts otherButtons:nil, is to initialise UIAlertView with otherButtonTitles (which can be nil), and iterate over the variadic arguments, as above:

+ (void)showWithTitle:(NSString *)title
              message:(NSString *)message
             delegate:(id)delegate
    cancelButtonTitle:(NSString *)cancelButtonTitle
    otherButtonTitles:(NSString *)otherButtonTitles, ...
{
    UIAlertView *alert = [[[UIAlertView alloc] initWithTitle:title
                                                     message:message
                                                    delegate:delegate
                                           cancelButtonTitle:cancelButtonTitle
                                           otherButtonTitles:otherButtonTitles] autorelease];

    // add your [alert setAlertViewStyle:UIAlertViewStylePlainTextInput] etc. as required here

    if (otherButtonTitles != nil) {
        va_list args;
        va_start(args, otherButtonTitles);
        NSString * title = nil;
        while(title = va_arg(args,NSString*)) {
            [alert addButtonWithTitle:title];
        }
        va_end(args);
    }

    [alert show];
}