Objective-C单例模式
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。http://www.2cto.com/uploadfile/Collfiles/20150314/20150314084245107.jpg[*]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 = [ init]; }); return sharedObject;}- (id)init{ if (self = ) { } return self;}+ (id)allocWithZone:(struct _NSZone *)zone{ return ;}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 = [ init]; }); return sharedObject;}+ (id)allocWithZone:(NSZone *)zone {return [ 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 = ) {}return self;}- (void)dealloc {;}@end
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