[IOS 下重溫設計模式] – Singleton

View Code

@interface Singleton : NSObject 
{

}

+ (Singleton *) sharedInstance;

- (void) operation;


@end

View Code

#import "Singleton.h"


@implementation Singleton


static Singleton *sharedSingleton_ = nil;

- (void) operation
{
// do something
  NSLog(@"Singleton");
}

+ (Singleton *) sharedInstance
{
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; // denotes an object that cannot be released
}

- (void) release
{
// do nothing
}

- (id) autorelease
{
return self;
}

@end

=============================

View Code

@interface MySingleton : Singleton
{

}

@end

View Code

@implementation MySingleton

- (id) init
{

return self; 
}

- (void) operation
{
// do something
  NSLog(@"MySingleton");
}

@end

=============================

client:

View Code

  Singleton *s = [MySingleton sharedInstance];

  [s operation];