iOS Basic Learning Log (vii) create a singleton with dispatch_once and use

Since Apple introduced Grand Central Dispatch (GCD)(Mac OS 10.6 and iOS4.0), there is a new way to create a singleton, which is to use the Dispatch_once function, of course, as the evolution progresses, There will be more and better ways to appear. Here's a brief introduction to how to create a singleton using Dispatch_once.

In development we will use Nsnotificationcenter, Nsfilemanager, etc. to get their instances through [Nsnotificationcenter defaultcenter] and [Nsfilemanager Defaultmanager] to get, in fact, this is a single case.

Let's take a look at the function void Dispatch_once (dispatch_once_t *predicate, dispatch_block_t block), where the first parameter predicate, This parameter is a predicate that checks whether the block of code represented by the second argument is called, and the second parameter is a block of code that will only be called once throughout the application. The code blocks in the Dispach_once function are only executed once and are thread-safe.

and then we're going to implement our own singleton, here is a Schoolmanager class that implements a singleton for this class

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2. + (Schoolmanager *) sharedinstance
4. {  
6.     static  schoolmanager *sharedmanager;  
8.       
10.     static  dispatch_once_t oncetoken;  
12. Dispatch_once (&oncetoken, ^{
14. Sharedmanager = [[Schoolmanager alloc] init];
16. });
20.     return  sharedmanager;  
22. }

So far , we have implemented a single case, everything is done, is not very simple!

Use the following method to obtain a unique instance:

[CPP]View Plaincopy

1. Schoolmanager *schoolmanager = [Schoolmanager sharedinstance];

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iOS Basic Learning Log (vii) create a singleton with dispatch_once and use