Objective-C单例模式

jiyuzi

单例类是一种特殊的类，在一个进程种只会存在一个该类的对象，在iOS应用中只会出现一个对象。这种设计模式在系统框架中许多地方都使用了，如NSFileManager、UIApplication等。

• 在ARC的环境下，接口文件为：////  DVISingleton.h////  Copyright (c) 2014 长沙戴维营教育. All rights reserved.//#import @interface DVISingleton : NSObject+ (instancetype)sharedSingleton;@end

  实现文件：

  ////  DVISingleton.m////  Copyright (c) 2014 长沙戴维营教育. All rights reserved.//#import "DVISingleton.h"@implementation DVISingleton+ (instancetype)sharedSingleton{    static DVISingleton *sharedObject = nil;    //线程安全，只允许执行依次    static dispatch_once_t onceToken;    dispatch_once(&onceToken, ^{        //使用父类的allocWithZone:方法创建对象        sharedObject = [[super allocWithZone:NULL] init];    });    return sharedObject;}- (id)init{    if (self = [super init]) {    }    return self;}+ (id)allocWithZone:(struct _NSZone *)zone{    return [self sharedSingleton];}www.2cto.com- (id)copy{    return self;}- (void)dealloc{}@end
  • 在非ARC环境下的实现文件：#import "DVISingleton.h"@implementation DVISingleton+ (instancetype)sharedSingleton{    static DVISingleton *sharedObject = nil;    //线程安全，只允许执行依次    static dispatch_once_t onceToken;    dispatch_once(&onceToken, ^{        //使用父类的allocWithZone:方法创建对象        sharedObject = [[super allocWithZone:NULL] init];    });    return sharedObject;}+ (id)allocWithZone:(NSZone *)zone {  return [[self sharedSingleton] retain];}- (id)copyWithZone:(NSZone *)zone {  return self;}- (id)retain {  return self;}- (unsigned)retainCount {  return UINT_MAX; //denotes an object that cannot be released}- (oneway void)release {  // never release}- (id)autorelease {  return self;}- (id)init {  if (self = [super init]) {  }  return self;}- (void)dealloc {  [super dealloc];}@end