title: Cannot call a class method with [self theMethod:]
body: <p>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.</p>
  
  <p><strong>Header File</strong></p>
  
  <pre><code>#import &lt;UIKit/UIKit.h&gt;
  
  @interface LoginViewController : UIViewController {
      //Declare Vars
  }
  - (IBAction) login: (id) sender;
  + (NSString *) md5Hash:(NSString *)str;
  @end
  </code></pre>
  
  <p><strong>Source File</strong></p>
  
  <pre><code>+ (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"];
  }
  </code></pre>