Object-C实现单例模式

头文件：

@interface PlotGallery : NSObject

{

NSMutableArray *plotItems;

}

 

+(PlotGallery *)sharedPlotGallery;

 

-(void)addPlotItem:(PlotItem *)plotItem;

 

-(void)sortByTitle;

-(NSUInteger)count;

-(PlotItem *)objectAtIndex:(NSUInteger)index;

 

@end

实现文件：

#import "PlotGallery.h"

 

@implementation PlotGallery

 

static PlotGallery *sharedPlotGallery = nil;

 

+(PlotGallery *)sharedPlotGallery

{

@synchronized(self)

{

if ( sharedPlotGallery == nil ) {

sharedPlotGallery = [[selfalloc] init];

}

}

returnsharedPlotGallery;

}

 

+(id)allocWithZone:(NSZone *)zone

{

@synchronized(self)

{

if ( sharedPlotGallery == nil ) {

return [super allocWithZone:zone];

}

}

returnsharedPlotGallery;

}

 

-(id)init

{

Class thisClass = [self class];

 

@synchronized(thisClass)

{

if ( sharedPlotGallery == nil ) {

if ( (self = [super init]) ) {

sharedPlotGallery = self;

plotItems  = [[NSMutableArray alloc] init];

}

}

}

 

returnsharedPlotGallery;

}

 

-(id)copyWithZone:(NSZone *)zone

{

returnself;

}

 

-(id)retain

{

returnself;

}

 

-(NSUInteger)retainCount

{

returnUINT_MAX;

}

 

-(oneway void)release

{

}

 

-(id)autorelease

{

returnself;

}

 

-(void)addPlotItem:(PlotItem *)plotItem

{

[plotItems addObject:plotItem];

}

 

-(NSUInteger)count

{

return [plotItemscount];

}

 

-(PlotItem *)objectAtIndex:(NSUInteger)index

{

return [plotItemsobjectAtIndex:index];

}

 

-(void)sortByTitle

{

[plotItems sortUsingSelector:@selector(titleCompare:)];

}

 

@end