Implementing a singleton in iOS

In iOS, the memory allocation method for all objects calls Allocwithzone, such as the constructor alloc, so overriding this method allows you to implement a singleton.

Xcode is pre-written to implement the code quick instructions, knock Dispatch_once will see. This is a singleton code with GCD implementations.

The implementation code is as follows:

?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

+(id)allocWithZone:(struct _NSZone *)zone {     static LYDemo * instance;     //是线程安全的，onceToKen默认是0     static dispatch_once_t onceToken;     //dispatch_once宏可以保证代码中的代码只会被执行一次。     dispatch_once(&onceToken, ^{         instance = [super allocWithZone:zone];     });     return instance; } //上面代码只是保证了这个类只能有一个实例，而易读性略差，我们应该模仿系统的单例方式。 +(instancetype)sharedDemo {     return [[self alloc]init]; }

To implement a single-case procedure:

1. Rewrite the Allocwithzone method and use GCD pre-written code block Dispatch_once snippet.

2. Create a method that starts with GKFX and mimics the system's singleton.