Cannot call a class method with [self theMethod:]

Question

I am trying to write a class method in Objective C. The project builds fine when I declare the method. But the build fails whenever I try to call the method. Here is my code.

Header File

#import <UIKit/UIKit.h>  @interface LoginViewController : UIViewController {     //Declare Vars } - (IBAction) login: (id) sender; + (NSString *) md5Hash:(NSString *)str; @end 

Source File

+ (NSString *) md5Hash:(NSString *)str {     const char *cStr = [str UTF8String];     unsigned char result[16];     CC_MD5( cStr, strlen(cStr), result );      return [NSString stringWithFormat:         @"%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X",         result[0], result[1], result[2], result[3],          result[4], result[5], result[6], result[7],         result[8], result[9], result[10], result[11],         result[12], result[13], result[14], result[15]         ]; } - (IBAction) login: (id) sender {         //Call the class method         [self md5Hash:@"Test"]; } 

Answer 1

You should call it like this:

[LoginViewController md5Hash:@"Test"]; 

Because it's a class (LoginViewController) method and not an instance (self) method.

Answer 2

Or you could do:

- (IBAction) login: (id) sender {         //Call the static method         [[self class] md5Hash:@"Test"]; } 

which should be exactly the same as calling [LoginViewController md5Hash:@"Test"] directly with the class name. Remember that md5Hash is a CLASS method, not an instance one, so you can't call it in objects (instances of the class), but from the class itself.