Single Case 01

1.

Code:

@interface Samnetworkingtool:nsobject

+ (instancetype) Sharenetworkingtool;

@end

@implementation Samnetworkingtool

static ID instance;

because of historical problems, each call to Alloc will be called first Allocwithzone

+ (instancetype) Allocwithzone: (struct _nszone *) zone{

static dispatch_once_t oncetoken;

dispatch_once (&oncetoken, ^{

//This function executes only once in the program

instance = [super Allocwithzone:zone];

});

return instance;

}

+ (ID) copywithzone: (struct _nszone *) zone{

return instance;

}

+ (instancetype) sharenetworkingtool{

return [[Selfalloc] init];

}

@end

Test:

-(void) Viewdidload {

[Super Viewdidload];

For (int i = 0; i< ; i++) {

Samnetworkingtool *tool = [Samnetworkingtool Sharenetworkingtool];

NSLog (@ "%@", tool);

}

[Selfperformselectorinbackground:@selector (Testdemo) Withobject:nil];

}

-(void) Testdemo {

Puts ("-----");

For (int i = 0; i< ; i++) {

Samnetworkingtool *tool = [Samnetworkingtool Sharenetworkingtool];

NSLog (@ "%@", tool);

}

}

Singleton implementation: ( two ways: Mutex (@synchronized (self))and one-time code (dispatch_once));

2.1 Mutex @synchronized(self):

<1>. Keep An instance of the global static in the. m file .

static ID _instance;

<2>. Override several methods (Allocwithzone: and Copywithzone:) and provide a class method for the outside world to access a unique instance.

(1) rewrite the Allocwithzone: method, Create a unique instance here ( note thread safety). This method is called inside the//alloc .

+ (instancetype) Allocwithzone: (struct _nszone *) Zone {

if (_instance = = nil) { // Prevent frequent lock - up

@synchronized(self) {

if (_instance = = nil) { // Prevent creation of multiple

_instance = [super Allocwithzone:zone];

}

}

}

return _instance;

}

(2) rewrite Copywithzone: method.

+ (ID) copywithzone: (struct _nszone *) zone

{

return _instance;

}

(3) provides 1 classes of methods to access unique instances of the outside world

+ (instancetype) Sharesingleton

{

if (!_instance) { // Prevent frequent lock - up

@synchronized(self) {

if (!_instance) { // prevents creation of multiple

_instance = [[Selfalloc] init];

}

}

}

return _instance;

}

2

Disposable Code (dispatch_once):

<1>. Keep An instance of the global static in the. m file .

static ID _instance;

<2>. Override several methods (Allocwithzone: and Copywithzone:) and provide a class method for the outside world to access a unique instance.

(1) rewrite Allocwithzone: method, Create a unique instance here ( note thread safety).

+ (ID) allocwithzone: (struct _nszone *) zone

{

static dispatch_once_t Oncetoken;

dispatch_once (&oncetoken, ^{

_instace = [super Allocwithzone:zone];

});

return _instace;

}

(2) rewrite Copywithzone: method.

+ (ID) copywithzone: (struct _nszone *) zone

{

return _instance;

}

(3) provides 1 classes of methods to access unique instances of the outside world

+ (instancetype) Sharesingleton

{

static dispatch_once_t Oncetoken;

dispatch_once (&oncetoken, ^{

_instace = [[Selfalloc] init];

});

return _instace;

}

Note : The implementation of the Singleton in ARC and MRC is slightly different . MRC's implementation of the single example is a few more memory management methods than ARC :

The MRC increases the implementation of the following methods :

-(Instancetype) retain {return self;}

-(Nsuinteger) retaincount { return 1;}

-(oneway void) Release {}

-(instancetype) autorelease { return self ;}

3. judging the current environment (ARC/MRC)

#if __has_feature (OBJC_ARC)

ARC

#else

Mrc

#endif

Note: The singleton is best to provide only one way to create a single case

such as creating a management class to access the network

#import "AFHTTPSessionManager.h"

@interface Samnetworkingtool: afhttpsessionmanager

+ (instancetype) Sharenetworkingmanager;

@end

#import "SAMNetworkingTool.h"

@implementation Samnetworkingtool

static ID _instance;

+ (instancetype) sharenetworkingmanager{

static dispatch_once_t oncetoken;

dispatch_once (&oncetoken, ^{

Nsurlsessionconfiguration *sett = [nsurlsessionconfiguration defaultsessionconfiguration];

sett.timeoutintervalforrequest = a;

Nsurl *baseurl = [nsurl urlwithstring:@ "http://c.m.163.com/nc/"];

_instance = [[samnetworkingtool alloc] initwithbaseurl: BaseUrl sessionconfiguration : sett];

});

return _instance;

}

Provides only one way to create this object,

Single Case 01