OBJECTIVE-C Series-Single case

The earth has only one, so declare a Earth object on it, you can not declare two AH! Similarly, sometimes a class can have only one object case, such as a server, just want to save to a in//face, this way, the next time you can take out the last saved data.

// use global variables to implement singleton mode

a global variable is defined here , and then the global variable is returned in the Singleton method, which can also implement a singleton pattern

Earth * global=nil;

The global variable is returned in the Singleton method, but the object is created when the first call is made

+ (Earth *) Defaultearth

{

if (global==nil) {

global = [[Earth alloc]init];

}

return global;

}

****************************************

implementing a singleton pattern with static local variables

+ (Earth *) Defaultearth

{

static Earth* obj=nil;

if (obj==nil) {

obj=[[Earth alloc]init];

}

return obj;

}

**************************************

Using GCD to realize single case, super simple

-(Earth *) Shareearth

{

static Earth *sharedearthinstance = nil;

static dispatch_once_t oncetoken;

dispatch_once(&oncetoken, ^{

Sharedearthinstance = [[self alloc] init];

});

return sharedearthinstance;

}

OBJECTIVE-C Series-Single case