Appcast.h

#import <Foundation/Foundation.h>

@interface Appcast : NSObject

+ ( id ) instance;
+ (void) post:(NSString *) message;

@end

Appcast.m

#import "Appcast.h"
#import <dispatch/dispatch.h>

@implementation Appcast

+ (id) instance {
    
    static id instance = nil;
    
    static dispatch_once_t onceToken;
    
    dispatch_once(&onceToken, ^{
        instance = [[self alloc]init];
    });

    return instance;
}

+ (void) post:(NSString *) message {
    [[NSNotificationCenter defaultCenter] postNotificationName:message
                                                        object:[self instance]];
}

@end

Observe.m

// Observe

[[NSNotificationCenter defaultCenter] 

    addObserver :self
    selector    :@selector(didGetNotification:)
    name        :nil
    object      :[Appcast instance]

];

// Post

[Appcast post:event.pre_message];