Sometimes, we need access of some object /data/ variable globally throughout the App. In that case, creating a singleton class which can be accessed through out the app is helpful.

App Delegate is a good example of singleton class. After googling for 2 days, i found a cool way to create singleton class using Macros. Let's suppose i have to create an HttpRequest Manager to handle all requests using only one instance .

call following line where you have to want to create the singleton class object.

SYNTHESIZESINGLETONFOR_CLASS(RequestManager);

and following is the class SynthesizeSingleton.h

#define SYNTHESIZE_SINGLETON_FOR_CLASS(classname) \
 \
static classname *shared##classname = nil; \
 \
+ (classname *)shared##classname \
{ \
    @synchronized(self) \
    { \
        if (shared##classname == nil) \
        { \
            shared##classname = [[self alloc] init]; \
        } \
    } \
     \
    return shared##classname; \
} \
 \
+ (id)allocWithZone:(NSZone *)zone \
{ \
    @synchronized(self) \
    { \
        if (shared##classname == nil) \
        { \
            shared##classname = [super allocWithZone:zone]; \
            return shared##classname; \
        } \
    } \
     \
    return nil; \
} \
 \
- (id)copyWithZone:(NSZone *)zone \
{ \
    return self; \
} \
 \