Singleton on iOS （ObjC实现单例模式）

Singleton on iOS （Obj-C实现单例模式）

参考地址：http://www.duckrowing.com/2010/05/21/using-the-singleton-pattern-in-objective-c/

static MyGizmoClass *sharedGizmoManager = nil;

+ (MyGizmoClass*)sharedManager
{
@synchronized(self) {
if (sharedGizmoManager == nil) {
[[self alloc] init]; // assignment not done here
}
}
return sharedGizmoManager;
}

+ (id)allocWithZone:(NSZone *)zone
{
@synchronized(self) {
if (sharedGizmoManager == nil) {
sharedGizmoManager = [super allocWithZone:zone];
return sharedGizmoManager; // assignment and return on first allocation
}
}
return nil; //on subsequent allocation attempts return nil
}

- (id)copyWithZone:(NSZone *)zone
{
return self;
}

- (id)retain
{
return self;
}

- (unsigned)retainCount
{
return UINT_MAX; //denotes an object that cannot be released
}

- (void)release
{
//do nothing
}

- (id)autorelease
{
return self;
}