Make yourself in such a way as - [NSArray arrayWithObjects:]; infinite parameters, separated, ending with zero by argument

Question

In Objective-C, I can do something like:

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

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

Answer 1

Declare a method like this in @interface :

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

Then in @implementation you 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... } 

va_list , va_start , va_arg and va_end are the standard C syntax for handling variables. Describing them is simple:

• va_list is a pointer to a list of variable arguments.
• va_start - Initializes va_list to indicate the first argument after the specified argument.
• va_arg - Displays the next argument from the list. You must specify the type of the argument (so va_arg knows how many bytes to retrieve).
• va_end - frees memory stored in the va_list data structure.

Read this article for a better explanation - Variable Argument Lists in Cocoa

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See also: "IEEE Std 1003.1 stdarg.h"

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Another example from Apple Technical Q & A QA1405 is 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 contents. va_end(argumentList); } } @end