Step 1: Open your XCode project and add a new class.
 
In your XCode > ‘Group & Files’ colum > Right click on the classes folder > Click ‘Add > New File..’ > Select ‘Objective-C class’ (ensure its a sub class of NSObject) > Click ‘Next’ > Enter the new class name (in this example, GlobalData) > Finish
 
Step 2: The .h file
 
@interface GlobalData : NSObject {
NSString *message; // global variable
}
 
@property (nonatomic, retain) NSString *message;
 
+ (GlobalData*)sharedGlobalData;
 
// global function
- (void) myFunc;
 
@end
 
 
Step 3: The .m file
 
#import "GlobalData.h"
 
@implementation GlobalData
@synthesize message;
static GlobalData *sharedGlobalData = nil;
 
+ (GlobalData*)sharedGlobalData {
    if (sharedGlobalData == nil) {
        sharedGlobalData = [[super allocWithZone:NULL] init];
 
	// initialize your variables here
	sharedGlobalData.message = @"Default Global Message";
    }
    return sharedGlobalData;
}
 
+ (id)allocWithZone:(NSZone *)zone {
	@synchronized(self)
	{
		if (sharedGlobalData == nil)
		{
			sharedGlobalData = [super allocWithZone:zone];
			return sharedGlobalData;
		}
	}
	return nil;
}
 
- (id)copyWithZone:(NSZone *)zone {
    return self;
}
 
- (id)retain {
    return self;
}
 
- (NSUInteger)retainCount {
    return NSUIntegerMax;  //denotes an object that cannot be released
}
 
- (void)release {
    //do nothing
}
 
- (id)autorelease {
    return self;
}
 
// this is my global function
- (void)myFunc {
	self.message = @"Some Random Text";
}
@end
 
 
Access Global:
#import "GlobalData.h"
 
Access Global Variable:
[GlobalData sharedGlobalData].message
 
Access Global Function:
[[GlobalData sharedGlobalData] myFunc];