Singleton Objects - Lazy ini

gistfile1.txt

Singleton Objects
Lazy initialization is common
@implementation FooController 

// #1
+ (FooController *)sharedInstance
{
static dispatch_once_t once; 
static FooController *instance; 
dispatch_once(&once, ^{
instance = [[FooController alloc] init]; 
return instance;
} @end


// #2
+ (FooController *)sharedInstance
{
 static FooController *instance;
 if (!instance) 
   instance = [[FooController alloc] init];
 return instance;
} 
@end

// #3

+ (FooController *)sharedInstance; // will create 
+ (FooController *)activeInstance; // won’t create 
+ (FooController *)sharedInstance
                   createIfNeeded:(BOOL)createIfNeeded;
@end