IOS開發中單例模式使用詳解

////  UserContext.h//  SingleDemo////  Created by andyyang on 9/30/13.//  Copyright (c) 2013 andyyang. All rights reserved.//#import <Foundation/Foundation.h>@interface UserContext : NSObject@property (nonatomic,retain) NSString *username;@property(nonatomic,retain)NSString *email;+(id)sharedUserDefault;@end

////  UserContext.m//  SingleDemo////  Created by andyyang on 9/30/13.//  Copyright (c) 2013 andyyang. All rights reserved.//#import "UserContext.h"static UserContext *singleInstance=nil;@implementation UserContext+(id)sharedUserDefault{    if(singleInstance==nil)    {        @synchronized(self)        {            if(singleInstance==nil)            {                singleInstance=[[[self class] alloc] init];                            }        }    }    return singleInstance;}+ (id)allocWithZone:(NSZone *)zone;{    NSLog(@"HELLO");if(singleInstance==nil){    singleInstance=[super allocWithZone:zone];}    return singleInstance;}-(id)copyWithZone:(NSZone *)zone{    NSLog(@"hello");    return singleInstance;}-(id)retain{    return singleInstance;}- (oneway void)release{}- (id)autorelease{    return singleInstance;}- (NSUInteger)retainCount{    return UINT_MAX;}@end

#import <Foundation/Foundation.h>#import "UserContext.h"int main(int argc, const char * argv[]){    @autoreleasepool {               UserContext *userContext1=[UserContext sharedUserDefault];        UserContext *userContext2=[UserContext sharedUserDefault];        UserContext *userContext3=[[UserContext alloc] init];        UserContext *userContext4=[userContext1 copy];        // insert code here...        NSLog(@"Hello, World!");            }    return 0;}

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