Make yourself a method such as -[NSArray arrayWithObjects:]; infinite parameters separed by , ended by nil on argument

Question

On Objective-C, I can do something like:

UIAlertView *av = [[UIAlertView alloc] initWith ... otherButtonTitles:@"button1", @"button2", nil];

Can I make a method for myself which takes as an argument these parameters separed by a comma... And if so how?

Answer 1

Declare the method like this in your @interface:

- (id)myObjectWithObjects:(id)firstObject, ... NS_REQUIRES_NIL_TERMINATION;

Then in the @implementation you would define it like this:

- (id)myObjectWithObjects:(id)firstObject, ...
{
    va_list args;
    va_start(args, firstObject);
    for (id arg = firstObject; arg != nil; arg = va_arg(args, id))
    {
        // Do something with the args here
    }
    va_end(args);

    // Do more stuff here...
}

The va_list, va_start, va_arg and va_end are all standard C syntax for handling variable arguments. To describe them simply:

• va_list - A pointer to a list of variable arguments.
• va_start - Initializes a va_list to point to the first argument after the argument specified.
• va_arg - Fetches the next argument out of the list. You must specify the type of the argument (so that va_arg knows how many bytes to extract).
• va_end - Releases any memory held by the va_list data structure.

Check out this article for a better explanation - Variable argument lists in Cocoa

---

See also: "IEEE Std 1003.1 stdarg.h"

---

Another example from the Apple Technical Q&A QA1405 - Variable arguments in Objective-C methods:

@interface NSMutableArray (variadicMethodExample)

- (void) appendObjects:(id) firstObject, ...; // This method takes a nil-terminated list of objects.

@end

@implementation NSMutableArray (variadicMethodExample)

- (void) appendObjects:(id) firstObject, ...
{
    id eachObject;
    va_list argumentList;
    if (firstObject) // The first argument isn't part of the varargs list,
    {                                   // so we'll handle it separately.
        [self addObject: firstObject];
        va_start(argumentList, firstObject); // Start scanning for arguments after firstObject.
        while (eachObject = va_arg(argumentList, id)) // As many times as we can get an argument of type "id"
            [self addObject: eachObject]; // that isn't nil, add it to self's contents.
        va_end(argumentList);
    }
}

@end