Objective-c Single case Mode singleton

List the referenced documents first:

Http://www.cnblogs.com/supercheng/archive/2012/11/26/singlemodal.html

http://arthurchen.blog.51cto.com/2483760/642536/

http://blog.csdn.net/duboleon/article/details/6337174

https://developer.apple.com/legacy/library/documentation/Cocoa/Conceptual/CocoaFundamentals/CocoaObjects/ Cocoaobjects.html#//apple_ref/doc/uid/tp40002974-ch4-sw32

Https://developer.apple.com/library/ios/documentation/General/Conceptual/DevPedia-CocoaCore/Singleton.html

"Big Talk design mode"

Http://www.cocoachina.com/industry/20130510/6168.html

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Singleton Singleton mode: guarantees that a class has only one instance and provides a global access point to access it.

Implementing a singleton pattern requires a focus on the case where multiple instances are created by multithreaded access.

The code that does not consider multithreading is as follows:

////MyManager.h//Singleton////Created by a chess on 15-3-7.//Copyright (c) A chess of 2015 years. All rights reserved.//#import<Foundation/Foundation.h>@interfacemymanager:nsobject{NSString*_namer;} @property (nonatomic,retain) NSString*name;+(ID) Sharedmymanager;//sharedxxx,defaultxxx,currentxxx@endCarryon -/3/Ten  +: -: the////MYMANAGER.M//Singleton////Created by a chess on 15-3-7.//Copyright (c) A chess of 2015 years. All rights reserved.//#import "MyManager.h"//creating Singleton ObjectsStaticMymanager *instance;@implementationMymanager@synthesizeName =_name;+(ID) sharedmymanager{if(Instance = =Nil) {Instance=[[Self alloc]init]; }    returninstance;}@end////main.m//Singleton////Created by a chess on 15-3-7.//Copyright (c) A chess of 2015 years. All rights reserved.//#import<Foundation/Foundation.h>#import "MyManager.h"intMainintargcConst Char*argv[]) {@autoreleasepool {Mymanager*tempobject1 =[Mymanager Sharedmymanager]; Mymanager*tempobject2 =[Mymanager Sharedmymanager]; NSLog (@"TempObject1 is%p", TempObject1); NSLog (@"TempObject2 is%p", TempObject2); }    return 0;}Output --Geneva- - xx:Wuyi:03.865singleton[752:303] TempObject1 is 0X100601C20 --Geneva- - xx:Wuyi:03.871singleton[752:303] TempObject2 is 0X100601C20Program ended with exit code:0

Consider multithreaded code, which is the recommended code:

////MyManager.h//Singleton////Created by a chess on 15-3-7.//Copyright (c) A chess of 2015 years. All rights reserved.//#import<Foundation/Foundation.h>@interfacemymanager:nsobject{NSString*_namer;} @property (nonatomic,retain) NSString*name;+(ID) Sharedmymanager;//sharedxxx,defaultxxx,currentxxx+(ID) Allocwithzone: (Nszone *) zone;-(ID) Copywithzone: (Nszone *) zone;-(ID) retain;-(Nsuinteger) retaincount;-(ID) autorelease;-(OneWayvoid) release;@end////MYMANAGER.M//Singleton////Created by a chess on 15-3-7.//Copyright (c) A chess of 2015 years. All rights reserved.//#import "MyManager.h"//creating Singleton ObjectsStaticMymanager *instance;@implementationMymanager@synthesizeName =_name;+(ID) sharedmymanager{@synchronized (self) {//The Synchronized keyword ensures that only one thread accesses the code at the same time            if(Instance = =Nil) {Instance=[[Self alloc]init]; }    }    returninstance;}+(ID) Allocwithzone: (Nszone *) zone{@synchronized (self) {if(Instance = =Nil) {Instance=[Super Allocwithzone:zone]; returninstance; }        returnNil; }}-(ID) Copywithzone: (Nszone *) zone{returnSelf//Make sure that the Copy object is unique. }-(ID) retain{returnSelf//Make sure the count is unique}-(Nsuinteger) retaincount{returnUint_max;}-(ID) autorelease{returnSelf ;}-(OneWayvoid) release{// do nothing}@end


There is also a gcd notation
/*
+ (ID) sharedmymanager{
Static dispatch_once_t once;//Ensure that once is used only once
Dispatch_once (&once,^{
if (instance = = null) {
instance = [[Self alloc]init];
})
return instance;
}
*/

Overriding these methods is to comply with the singleton rule when declaring an instance in other ways, that is, there is only one object.

Objective-c Single case Mode singleton