Cocoa: Calling a method from AppDelegate.m - objective-c

Question

In order to better understand the startup, event queue, and methods within my application I'm trying to write a program that does two things: Play a beep at the startup and every time the user hits a button. So far it only plays when the user hits the button. I know there may be multiple ways to get the startup beep to play, but in order to work with initialization code I want to do it by calling my beep method from within the applicationDidFinishLaunching method of the AppDelegate.m file.
Here is my code:
Log.h
#import <Cocoa/Cocoa.h>
#interface Log : NSObject {
IBOutlet id button;
}
-(void)beepAndLog;
-(IBAction)buttonPressed:(id)sender;
#end
Log.m
#import "Log.h"
#implementation Log
-(void)beepAndLog {
NSLog(#"The Method Was Called!");
NSBeep();
}
-(IBAction)buttonPressed:(id)sender {
[self beepAndLog];
}
#end
And the applicationDidFinishLaunching method looks like this:
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
// Insert code here to initialize your application
[Log beepAndLog];
}
In the applicationDidFinishLaunching method, however, XCode warns me that
'Log' may not respond to '+beepAndLog'
and indeed, there is no beep and the log reads as follows:
MethodResponse[11401:a0f] +[Log
beepAndLog]: unrecognized selector
sent to class 0x100002100
("MethodResponse" is the name of my project, btw)
I'm unsure why Log wouldn't respond to beepAndLog, seeing as that's one of its methods. Am I calling it incorrectly? I have a feeling this will be painfully obvious to you more experienced people. I'm a newbie. Any help would be appreciated! Thanks!

Answer 1

There are two possibilities. Either you defined beepAndLog as an instance method, when you wanted a class method, or you want to call it on an instance when you called it on the class.
To change it to a class method, change the header to read:
+(void)beepAndLog;
and the implementation:
+(void)beepAndLog {
NSLog(#"The Method Was Called!");
NSBeep();
}
For the other solution, make sure you have an instance of class Log around (probably a singleton), and do something like:
[[Log logInstance] beepAndLog];
from your notification method. The Log class would need to look something like this:
Log.h:
#import <Cocoa/Cocoa.h>
#interface Log : NSObject {
IBOutlet id button;
}
+(Log *)logInstance;
-(void)beepAndLog;
-(IBAction)buttonPressed:(id)sender;
#end
Log.m:
#import "Log.h"
Log *theLog = nil;
#implementation Log
+(Log *)logInstance
{
if (!theLog) {
theLog = [[Log alloc] init];
// other setup (like hooking up that IBAction)
}
return theLog;
}
-(void)beepAndLog {
NSLog(#"The Method Was Called!");
NSBeep();
}
-(IBAction)buttonPressed:(id)sender {
[[Log logInstance] beepAndLog];
}