IOS设计模式之一：单例模式

#import <Foundation/Foundation.h>

@interface Singleton : NSObject
+(Singleton *) instance;
@end

@implementation Singleton
+(Singleton *) instance
{
static Singleton *sharedSingleton_ = nil;
@synchronized(self){
if(sharedSingleton_ == nil){
sharedSingleton_ = [NSAllocateObject([self class], 0, NULL) init];
}
}
return sharedSingleton_;
}

+ (id) allocWithZone:(NSZone *)zone
{
return [[self sharedInstance] retain];
}

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

- (id) retain
{
return self;
}

- (NSUInteger) retainCount
{
return NSUIntegerMax;
}

-(void)release
{
[super release];
}

- (id) autorelease
{
return self;
}

@end

static RootViewController* sharedRootController = nil;

+(RootViewController *) sharedController{
@synchronized(self){
if (sharedRootController == nil) {
sharedRootController = [[self alloc] init];
}
}
return  singleController;
}